Journal of Trauma & Dissociation ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/wjtd20 The Prevalence of Depersonalization-Derealization Disorder: A Systematic Review Jinyan Yang, L. S. Merritt Millman, Anthony S. David & Elaine C.M. Hunter To cite this article: Jinyan Yang, L. S. Merritt Millman, Anthony S. David & Elaine C.M. Hunter (2023) The Prevalence of Depersonalization-Derealization Disorder: A Systematic Review, Journal of Trauma & Dissociation, 24:1, 8-41, DOI: 10.1080/15299732.2022.2079796 To link to this article: https://doi.org/10.1080/15299732.2022.2079796 © 2022 The Author(s). Published with license by Taylor & Francis Group, LLC. Published online: 14 Jun 2022. Submit your article to this journal Article views: 8169 View related articles View Crossmark data Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=wjtd20 JOURNAL OF TRAUMA & DISSOCIATION 2023, VOL. 24, NO. 1, 8–41 https://doi.org/10.1080/15299732.2022.2079796 The Prevalence of Depersonalization-Derealization Disorder: A Systematic Review Jinyan Yang a, L. S. Merritt Millman b, Anthony S. David a, and Elaine C.M. Hunter a aDivision of Psychiatry, University College London, London, UK; bDepartment of Psychology, Goldsmiths, University of London, London, UK ABSTRACT ARTICLE HISTORY Depersonalization-Derealization disorder (DDD) is a psychiatric Received 10 June 2021 condition characterized by persistent feelings of detachment Accepted 11 November 2021 from one’s self and of unreality about the outside world. This KEYWORDS review aims to examine the prevalence of DDD amongst differ- Dissociative disorders; ent populations. A systematic review protocol was developed epidemiology; systematic before literature searching. Original articles were drawn from review three electronic databases and included only studies where prevalence rates of DDD were assessed by standardized diag- nostic tools. A narrative synthesis was conducted. Twenty-three papers were identified and categorized into three groups of participants: general population, mixed in/outpatient samples, and patients with specific disorders. The prevalence rates ran- ged from 0% to 1.9% amongst the general population, 5–20% in outpatients and 17.5–41.9% in inpatients. In studies of patients with specific disorders, prevalence rates varied: 1.8–5.9% (sub- stance abuse), 3.3–20.2% (anxiety), 3.7–20.4% (other dissociative disorders), 16.3% (schizophrenia), 17% (borderline personality disorder), ~50% (depression). The highest rates were found in people who experienced interpersonal abuse (25–53.8%). The prevalence rate of DDD is around 1% in the general population, consistent with previous findings. DDD is more prevalent amongst adolescents and young adults as well as in patients with mental disorders. There is also a possible relationship between interpersonal abuse and DDD, which merits further research. Introduction Depersonalization (DP) and derealization (DR) are symptoms characterized by, respectively, feelings of unreality and detachment from one’s self and one’s surroundings (American Psychiatric Association, 2013). Depersonalization and derealization (DP/DR) symptoms can occur as transient experiences in otherwise healthy individuals at times of stress or physical exhaustion and have been used as terms to describe the phenomenon of “burnout” (Maslach & Jackson, 1981). On the other hand, Depersonalization-Derealization Disorder (DDD) occurs when this symptom cluster is persistent and distressing and is CONTACT Elaine C.M. Hunter e.hunter@ucl.ac.uk Department of Psychiatry, University College London, 6/F, Maple house, 149 Tottenham Court Rd, London W1T 7NF, UK © 2022 The Author(s). Published with license by Taylor & Francis Group, LLC. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way. JOURNAL OF TRAUMA & DISSOCIATION 9 paired with functional impairment, rendering it a clinical diagnosis alongside other mental disorders or as a primary condition (American Psychiatric Association, 2013). There is limited literature regarding the prevalence rate of DDD. A recent review focusing on the epidemiology of DP/DR both as a symptom and as a disorder was conducted by Hunter et al. (2004), which included relevant papers published between 1966 and October 2002. According to this review, the prevalence rate of DDD was 1–2% in community samples when using interviews as the diagnostic tool, while transient symptoms of DP/DR were more prevalent in the general population with lifetime rates of 26–74%. Prevalence rates likely vary due to inconsistent definitions of DP/DR as a symptom or as a clinically significant disorder, paired with the use of a range of diagnostic tools. In order to evaluate as many studies as possible that contained some data on the prevalence of DP/DR, Hunter et al. (2004) did not set strict exclusion criteria for the quality of the studies under review. As a result, the previous review may include some studies of lower quality, potentially influencing the strength of the evidence. Therefore, this review aims to update the previous work, adopting a more systematic approach following PRISMA guidelines. Two clinical interviews are commonly used when making a DDD diagnosis in clinical practice: the Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID-D; Steinberg, 1994) and the Dissociative Disorders Interview Schedule (DDIS; Ross et al., 1989). The SCID-D is a semi-structured interview (Steinberg, 1994) and the DDIS is a clinician-administered structured inter- view (Ross et al., 1989). Both are used to identify dissociative disorders according to the DSM-IV (Ross et al., 1989; Steinberg, 1994). In order to capture all potentially useful data, studies using either one of these interviews were included, as well as studies that incorporated a standardized scale with a clinical cut-off score. The Cambridge Depersonalization Scale (CDS; Sierra & Berrios, 2000) and the depersonalization subscale of the Dissociative Experiences Scale (DES; Bernstein & Putnam, 1986) are two of the most frequently used standardized diagnostic scales of DDD that include a clinical cut-off score. Simeon et al. (1998) also suggest that the taxon version of the DES, consisting of 8 items regarding pathological dissociation in the DES (Waller et al., 1996), could be more useful than the mean DES score when detecting DDD (Simeon et al., 1998). Our systematic review aims to describe the prevalence rates of DDD in a range of populations. To address this, we have reviewed quantitative studies published since October 2002 that provide relevant information about the prevalence rates of DDD and conducted a narrative synthesis to explore the findings from the selected studies. 10 J. YANG ET AL. Method A systematic review protocol in PROSPERO format was developed and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. The review protocol is shown in Appendix. Search strategy The search was limited to studies published in English after October 2002 but geographical locations were not limited. Three electronic databases were initially searched and screened in March 2020: PsycINFO, MEDLINE and Web of Science. Grey literature was also screened in Google Search. The results from these sources were combined with duplica- tions removed. The search process was conducted by two independent reviewers to minimize error and repeated in February 2021 to include any eligible papers published since March 2020. The original search history is shown in Appendix. Search terms When defining the search terms, two main concepts were identified: 1, “depersonalization/derealization,” and 2, “prevalence.” For each concept, the Boolean operator “OR” was used to group all of the search terms. Both text words (free-text searches) and relevant subject terms (MeSH terms) were used as search terms and the results were combined within each concept. Concept 1 (depersonalization, derealization, depersonalization dis- order, derealization disorder) and concept 2 (epidemiolog*, prevalen*, occurrence, frequency) were combined using the Boolean operator “AND.” To cover all potential literature, we used truncation and searched both UK and US spellings. Inclusion/ exclusion criteria We only included quantitative studies that provided or allowed for the calcu- lation of prevalence rates. Reviews were excluded although reference lists were manually screened to retrieve any other relevant studies. Studies were excluded if: (a) they focused only on the relationship between DDD and its risk factors; (b) they only provided prevalence rates of other mental disorders or DP/DR symptoms; (c) they provided prevalence rates of DDD without use of a diagnostic interview or a standardized measure and clinical cut-off scores; (d) they focused on burnout or burnout syndrome rather than DDD. JOURNAL OF TRAUMA & DISSOCIATION 11 The standardized clinical interviews for depersonalization include the SCID-D (Steinberg, 1994) and the DDIS (Ross et al., 1989). Clinically significant DDD can also be indicated by a cut-off score of ≥70 in the CDS (Sierra & Berrios, 2000) or by a sub-scale score of ≥30 in the Derealization/ Depersonalization sub-scale of the DES (Bernstein & Putnam, 1986). Studies using the CDS-2, with a cut-off score of 3 (Michal, Zwerenz, et al., 2010; Sierra & Berrios, 2000), the CDS-9, with a cut-off score of 19 (Michal et al., 2004; Sierra & Berrios, 2000), or the taxon version of the DES, with a cut-off score of 13 (Bernstein & Putnam, 1986) were also eligible for inclusion. Any translated versions of the above interviews and scales that were validated and provided a cut-off score were also accepted. Studies using other scales were excluded. Procedure Two independent reviewers conducted study selection, quality assess- ment and data extraction process. In each phase, any discrepancies between the two reviewers were resolved through discussion with a third reviewer. After removing duplicates in the initial database searches, the two indepen- dent reviewers screened titles and abstracts of the literature against inclusion criteria and then retrieved full texts of potential studies to assess their elig- ibility. Reasons for exclusion were recorded. Then, two reviewers assessed the quality of eligible studies indepen- dently, using an adapted version of the Quality assessment checklist for prevalence studies (Nguyen et al., 2016). The adapted checklist consists of nine items that assess the risk of bias in nine domains with one summary item indicating the overall risk of bias (Nguyen et al., 2016). It was selected as it provides more specific criteria regarding the level of risk of bias than the original checklist (Hoy et al., 2012). A score of zero in each item indicated low risk and 1 indicated high risk. The overall risk of bias was indicated by the total score (Low risk: 0–3; Moderate risk: 4–6; High risk: 7–9). Before merging the results from the reviewers, the inter-rater reliability was calculated by an intraclass correlation coefficient. Only papers at low or moderate risk of bias were included in the data extraction process, and a standardized form adapted from the Cochrane Data collection form template was used (Higgins, 2008). A narrative synthesis was conducted to explore the findings from the included studies. 12 J. YANG ET AL. Results Study selection In total, 1,786 papers were identified in the initial search, with 1151 remaining after removing duplicates. The PRISMA flow diagram for a summary of the selection process is shown in Figure 1. Sixty-seven potential papers were identified and the full texts were assessed for eligibility. In the study by Baker et al. (2003), all participants were DDD patients recruited from a specialist clinic, so this paper was excluded in our review. Additionally, three eligible papers, (Foote et al., 2008; Michal, Wiltink, et al., 2010; Tschan et al., 2013) were excluded as the same samples were used in three other included papers (Foote et al., 2006; Michal et al., 2009; Michal, Wiltink, Till, Wild, Blettner, et al., 2010). When screening full texts, we excluded one paper (Duffy, 2000) due to the discrepancy between the publication year of this paper presented in the database (2002) and presented in the paper (2000). When repeating the search process in February 2021, we found one eligible paper (Schlax et al., 2020) published since March 2020. Thus, 23 papers were identified and included in the following analysis. Study characteristics The range of publication dates was from 2006 to 2020. There was a good international distribution of the studies including Turkey (n = 5), Germany (n = 4) and the United States (n = 3). Other studies were from Canada (n = 1), Israel (n = 1), Mexico (n = 1), Northern Ireland (n = 1), Puerto Rico (n = 1), Serbia (n = 1), Spain (n = 2), Switzerland (n = 1), and the United Kingdom (n = 1). There was also one transcultural study (Sierra et al., 2006). Most studies used structured or semi-structured interviews to obtain a diagnosis of DDD, such as the DDIS (n = 4) or the SCID-D (n = 8). Ten papers used the CDS (n = 6), the CDS-2 (n = 3) or the CDS-9 (n = 1). Only one study used the Derealization/Depersonalization sub-scale of the DES. Sample characteristics Sample sizes ranged from 20 to 13,182. In most of the studies, the mean age of participants ranged from 30 to 50 years (n = 17) and the proportion of female participants was above 50% (n = 18). Two studies did not report mean age of the sample (Gonzalez-Torres et al., 2010; Mueller-Pfeiffer et al., 2012) and two studies did not give the percentage of females (Gonzalez-Torres et al., 2010; Michal, Wiltink, Till, Wild, Blettner, et al., 2010). Nine papers assessed the prevalence rate of DDD amongst the general population. Five studies were conducted amongst patients with mixed or non- specified disorders, with participants being outpatients (n = 2), inpatients JOURNAL OF TRAUMA & DISSOCIATION 13 Figure 1. PRISMA flow diagram. (n = 1) and mixed or unspecified patients (n = 2). Twelve papers evaluated the prevalence of DDD amongst patients with specific disorders or conditions, including anxiety disorders (n = 4), dissociative spectrum disorders (n = 2), substance use disorders (n = 2), interpersonal abuse (n = 2), borderline personality disorder (n = 1), schizophrenia or schizophrenia spectrum dis- orders (n = 1) and depression (n = 1). However, there are three studies that involved two or three specific groups (Aponte-Soto et al., 2019; Gonzalez- Torres et al., 2010; Somer et al., 2015). 14 J. YANG ET AL. Quality assessment Most of the studies were at low risk (n = 15) and the remaining papers showed moderate risk (n = 8). We therefore included all 23 papers in our analysis. The intraclass correlation coefficient was 0.947, indicating excellent inter-rater reliability. Results: general population Table 1 presents the study characteristics and results of nine studies conducted amongst the general population. The prevalence rates of DDD were similar across five studies (Gonzalez- Torres et al., 2010; Johnson et al., 2006; Michal et al., 2009; Michal, Wiltink, Till, Wild, Blettner, et al., 2010; Schlax et al., 2020), ranging from 0.76% (Schlax et al., 2020) to 1.9% (Michal et al., 2009), even with sample sizes varying from 172 (Gonzalez-Torres et al., 2010) to 13,182 (Schlax et al., 2020). There were a few outliers. Aponte-Soto et al. (2019) found that the prevalence rate was 0% among a sample of 40 adults. Beyond this, the prevalence rate was 9.7% amongst a community adult sample in Israel (Somer et al., 2015), inconsistent with the general trend of ~1% rates. Additionally, in two studies conducted in adolescents (Michal et al., 2015) and undergraduate students (Myers & Llera, 2020), the prevalence rates were 11.9% and 11%, respectively. It should be noticed that there are potential overlaps between the participants in the study by Michal, Wiltink, Till, Wild, Blettner, et al. (2010) and the study by Schlax et al. (2020), as they both investigated participants from the Gutenberg Health Study. Results: patients with non-specific or mixed disorders Table 2 presents the study characteristics and results of five studies conducted among patients with unspecified or mixed disorders. Outpatients Two studies reported DDD prevalence rates among adult outpatients with unspecified or mixed disorders, varying from 5% (Foote et al., 2006) to 20% (Dorahy et al., 2006). The difference between the prevalence rates could be due to the small sample size of 20 patients in the Dorahy et al. (2006) study and, although these were outpatients, they were described as complex in presentation. JOURNAL OF TRAUMA & DISSOCIATION 15 Table 1. Study characteristics of studies involving the general population. DP/DR prevalence Authors & Prevalence (%) among Year of Mean age (SD) / assessment Results from general publication Country Population Sample size age range % female (n) method Cut-off score original papers Notes population Myers & United College psychology N = 198 M = 19.72; 72% (1% CDS 70 n = 22 participants 11% Llera States undergraduates SD = 2.32 gender (11%) reported (2020) variant/non- experiencing conforming, clinical levels of 27% male) dissociation. Michal Germany Pupils aged 12– N = 3,809 - No DP: M = 15.6; 51.7% CDS-2 3 (≥ 3) n = 452 (11.9%) 11.9% et al. 18 years SD = 1.7. (n = 1971) pupils aged 12– (2015) - DP: M = 15.8; - No DP: 18 years scored SD = 1.6 51.1% 3 or higher in (n = 1716) CDS-2. - DP: 56.4% (n = 255) Michal, Germany Randomly selected N = 4,912; - CDS-2 < 3 Not given CDS-2 ≥ 3 n = 41 (0.8%) 0.8% Wiltink, community sample **5,000 (n = 4859): participants Till, aged 35–74 enrolled participants M = 55.4; scored on or Wild, in Gutenberg Health were SD = 10.9. higher than 3 in Blettner, Study from enrolled but - CDS-2 >/ = 3 CDS-2, et al. April 2007 to only 4912 (n = 41): indicating (2010) October 2008 completed M = 53.3; a clinically the survey SD = 10.0 significant DDD Schlax Germany German general N = 13 182; M = 54.8; 49.5% CDS-2 ≥ 3 n = 100 (0.76%) 0.76% et al. population aged **15 010 SD = 10.9 (n = 6,526) participants (2020) 35–74 enrolled in participants scored on or Gutenberg Health were higher than 3 in Study from enrolled but CDS-2 April 2007 to only 13182 April 2012 included in the analysis (Continued) 16 J. YANG ET AL. Table 1. (Continued). DP/DR prevalence Authors & Prevalence (%) among Year of Mean age (SD) / assessment Results from general publication Country Population Sample size age range % female (n) method Cut-off score original papers Notes population Michal Germany German general N = 1,287 Total sample: 54.5% CDS-9 19(≥19) n = 25 (1.9%) 1.9% et al. population M = 48.9; - DP-C participants (2009) SD = 18.3; (clinical DP): scored in the range = 14–90. 64% range of - DP-C (clinical - DP-I clinically DP): M = 50.4; (impairment significant DDD/ SD = 17.7. caused by - DP-I DP): 61.6% (impairment caused by DP): M = 55.2; SD = 17.8 Gonzalez- Spain (1) Patients with N = 392: Overall: Not given CDS 71 (1) Among 141 ** There were 1.16% Torres schizophrenia or - patients: Median = 30.0, (Spanish patients, n = 24 errors in et al. schizophrenia n = 147 interquartile version) (17%) had DDD calculation in (2010) spectrum disorders - first-degree range = 24–42 according to the original paper. (2) First-degree relatives: - Patients: cut-off point of Correct healthy relatives n = 73 Median = 32, 71. prevalence with no psychiatric - control interquartile (2) Among 71 rates are listed history subjects: range = 25–40 relatives, n = 1 as follow: (3) healthy controls n = 172 - Relatives: (1%) had DDD (1) patients: 24/ from the general Median = 35.5, according to the 147 = 16.3% population interquartile cut-off point of (3) controls: 2/ range = 28– 71. 172 = 1.16%. 43.3 (3) Among 172 - Controls: controls, n = 2 Median = 27, (3%) had DDD interquartile according to the range = 23– cut-off point of 40.3 71. (Continued) JOURNAL OF TRAUMA & DISSOCIATION 17 Table 1. (Continued). DP/DR prevalence Authors & Prevalence (%) among Year of Mean age (SD) / assessment Results from general publication Country Population Sample size age range % female (n) method Cut-off score original papers Notes population Aponte- Puerto Hispanic adults with N = 80 M = 31.00; 65% (n = 52) CDS 70 (>70) (1) 25% of HIA **Original paper 0% Soto Rico and without - HIA: n = 40 SD = 9.9; - HIA: 65% (Spanish group scored > didn’t report et al. a history of - CCG: n = 40 range = 21–65 (n = 26) version) 70 on CDS. specific number (2019) interpersonal abuse: - CCG: 65% (2) No of participants (1) participants with (n = 26) participants diagnosed with a history of scored >70 on DDD interpersonal abuse CDS in the CCG (HIA); group. (2) control community group (CCG) without HIA Somer Israel (1) Opiate use disorder N = 261 - Arab women: 59% (n = 154) DDIS Meets DDIS (1) n = 43 (53.8%) 9.7% et al. patients - Arab M = 33.29; - Arab criteria Arab women (2015) (2) Arab women women: - OUD patients: women for DDD subjected to subjected to n = 80; M = 32.44; group: 100% diagnosis violence had domestic violence - OUD - nonclinical: (n = 80) DDD. (3) Non-clinical patients: M = 34.80 - OUD (2) n = 4 (5.9%) controls from n = 68; patient opiate use a community - Nonclinical group: 5.9% disorder sample (graduate participants: (n = 4) patients had students and their n = 103 - nonclinical DDD. friends and family Israeli group: (3) n = 10 (9.7%) members) 68% (n = 70) non-clinical controls had DDD Johnson United Adults in the N = 658 M = 33.1; SD = 2.9 53.0% (n = 349) SCID-D Meets DSM-IV n = 5 (0.8%) 0.8% et al. States community criteria for participants had (2006) DDD DDD, including 3 diagnosis females and 2 males. aWe recalculated the prevalence rates of DDD for all included papers. When the original papers had calculation errors in prevalence rates, we reported the correct prevalence rates in the results. We included patients with mixed DDD (i.e. dissociative amnesia+ Depersonalisation/ Derealisation) when calculating the prevalence rates. The median and interquartile range of age were reported if the original paper didn’t provide mean age (SD) or age range of the sample. bCDS = Cambridge Depersonalisation Scale; CDS-2 = 2-item version Cambridge Depersonalisation Scale; CDS-9 = 9-item version Cambridge Depersonalisation Scale; DDIS = Dissociative Disorders Interview Schedule; SCID-D = Structured Clinical Interview for DSM-IV Dissociative Disorders 18 J. YANG ET AL. Inpatients In a transcultural study (Sierra et al., 2006), participants were psychiatric inpatients from three countries: United Kingdom (n = 31), Spain (n = 68), and Colombia (n = 41), assessed using the CDS. Reported prevalence rates were 41.9%, 35.8% and 17.5%, respectively. Mixed or unspecified patients Similar prevalence rates of DDD were found in mixed or unspecified patients: 6% in Mexico (García et al., 2006) and 4.4% in Switzerland (Mueller-Pfeiffer et al., 2012). Results: patients with specific disorders See Table 3. According to the nature of the disorders or conditions, similar studies were grouped together. Anxiety disorders Four studies provided DDD prevalence amongst patients with anxiety dis- orders: patients with panic disorder (Mendoza et al., 2011; Ural et al., 2015), patients with obsessive-compulsive disorder (Belli et al., 2012) and patients with social anxiety disorder (Belli et al., 2017). Three studies were conducted in Turkey using the SCID-D (Belli et al., 2017, 2012; Ural et al., 2015) and one was conducted in Spain using the CDS (Mendoza et al., 2011). The prevalence rates ranged from 3.3% (Ural et al., 2015) to 20.2% (Mendoza et al., 2011). In those Turkish studies, the prevalence rates were 3.3% in panic disorder (Ural et al., 2015), 6.3% in social anxiety disorder (Belli et al., 2017), and 10.3% in obsessive-compulsive disorder (Belli et al., 2012). We included patients diagnosed with DDD as well as other dissociative disorders (i.e. dissocia- tive amnesia + depersonalization) when calculating the prevalence in the two studies (Belli et al., 2017, 2012). Ural et al. (2015) reported the number of patients with DDD only, hence the prevalence rate was likely to be underestimated. However, the proportions of patients only diagnosed with DDD were relatively consistent across those three studies: 3.3% (Ural et al., 2015), 5.3% (Belli et al., 2017), and 3.84% (Belli et al., 2012). For panic disorders specifically, the prevalence rate is much higher in the Spanish population (20.2%; Mendoza et al., 2011) than the Turkish population (3.3%; Ural et al., 2015). Dissociative spectrum disorders There were two studies conducted among patients with dissociative spectrum disorders. However, there was a large discrepancy in the prevalence of DDD between these two populations, at 3.7% in patients with conversion disorder (Yayla et al., 2015) and 20.4% in patients with non-epileptic seizures (Mitchell et al., 2012). JOURNAL OF TRAUMA & DISSOCIATION 19 Substance use disorders Two studies explored the prevalence of DDD in patients with substance use disorders. The prevalence rates were 1.8% in the Turkish sample with alcohol dependency (Evren et al., 2007), and 5.9% in the Israeli sample with opiate use disorder (Somer et al., 2015). Most of the patients in these two studies were males, with only 5.9% females in both studies. Interpersonal abuse The prevalence of DDD assessed by the DDIS was 53.8% in women who had experienced domestic violence (Somer et al., 2015). Aponte-Soto et al. (2019) found a lower prevalence rate of 25% using the CDS among a sample of 40 adults with a history of interpersonal abuse. Other specific disorders Three studies examined the prevalence of DDD in other specific disorders. Gonzalez-Torres et al. (2010) found prevalence rates of DDD to be 16.3% in Spanish inpatients with schizophrenia or schizophrenia spectrum disorders, with 1.4% of their first-degree relatives also meeting diagnostic criteria for DDD. Another study in Serbia (Žikić et al., 2009) found the prevalence of DDD was 47.6% in people with depression, and a study of 21 Canadian outpatients with borderline personality disorder (Korzekwa et al., 2009) detected a prevalence rate of 19%, assessed by the SCID-D. Results: prevalence assessment tools We examined prevalence rates of DDD in each study according to the type of assessment tools used (self-reported scales versus diagnostic interviews). See Table 4 Discussion A systematic review was conducted to examine the prevalence of DDD amongst different populations. Twenty-three studies dating from October 2002 to February 2021 were identified. The studies were mainly conducted amongst three types of populations (although some incorporated more than one type) including the general population, patients with non- specific or mixed disorders, and patients with specific disorders. The preva- lence rate amongst the general population was relatively consistent across studies, with an estimate of around 1% (0.76–1.9%; Aponte-Soto et al., 2019; Schlax et al., 2020). The findings amongst patients with specific disorders or unspecified disorders were mixed; however, it is clear that DDD is more prevalent in patients with mental health conditions, as compared to the general population. For the studies conducted amongst the patients with 20 J. YANG ET AL. Table 2. Study characteristics of studies involving patients with mixed or unspecified disorders. Authors & Mean age Prevalence Prevalence Year of (SD) /age assessment Results from original among Patient type publication Country population Sample size range % female (n) method Cut-off score papers Notes patients (%) Outpatients Dorahy Northern Ireland adult psychiatric N = 20 M = 40.7; 95% (19) DDIS Meets DDIS (1) n = 2 (10%) **new prevalence = 20% et al. patients aged SD = 8.8; criteria for patients diagnosed (2 + 2)/20 = 20% (2006) 18–65 range = DDD diagnosis with 26–57 depersonalisation disorder, (2) n = 2 (10%) patients with depersonalisation disorder and dissociative amnesia Foote et al. United States inner-city N = 82 M = 37.4; 64% (147 of DDIS Meets DDIS Among 82 patients 5% (2006) outpatient ** 231 SD = 11.4 231) criteria for who were psychiatric eligible (for entire DDD diagnosis interviewed met population participants sample of the criteria for aged 18–65 in original 231) a DSM-IV sample, but dissociative only 82 were disorder diagnosis, interviewed 4 (5%) patients with the had a diagnosis of DDIS depersonalisation disorder Inpatients (Continued) JOURNAL OF TRAUMA & DISSOCIATION 21 Table 2. (Continued). Authors & Mean age Prevalence Prevalence Year of (SD) /age assessment Results from original among Patient type publication Country population Sample size range % female (n) method Cut-off score papers Notes patients (%) Outpatients Sierra et al. United Kingdom, psychiatric N = 140; UK: M = 38.52; 47.9% (67) CDS (English 71 (>70) (1)13 (41.9%) patients 41.9% in UK (2006) Spain, and inpatients - n = 31 SD = 13 - UK: version for UK from UK scored inpatients; Colombia aged 18–65 from United Spain: 45.2% (14) group and above 70 in CDS 35.8% in Kingdom M = 35.13; - Spain: Spanish (2)24 (35.8%) Spain - n = 68 SD = 9 44.1% (30) version for patients from inpatients; from Spain Colombia: - Spanish and Spain scored 17.5% in - n = 41 M = 33.78, Colombia: Colombian above 70 in CDS Colombia from SD = 13 56.1% (23) groups) (3)7 (17.5%) inpatients Colombia patients from Colombia scored above 70 in CDS Mixed or unspecified patients Not mentioned Garcia Mexico Mexican N = 100 M = 32.4; 63% (63) DDIS Meets DDIS n = 6 (6%) patients 6% et al. psychiatric SD = 12.5; criteria for diagnosed with (2006) patients range = DDD diagnosis depersonalisation receiving 18–63 disorder treatment aged 18–63 Outpatients Mueller- Switzerland psychiatric N = 160 Median = 32.0 67.3% (107) SCID-D Meets DSM-IV n = 7 (out of 4.4% and day care Pfeiffer outpatients criteria for a possible 160) patients et al. and day care DDD diagnosis individuals (2012) patients diagnosed with depersonalisation disorder (4.4%), and all are female aWe recalculated the prevalence rates of DDD for all included papers. When the original papers had calculation errors in prevalence rates, we reported the correct prevalence rates in the results. We included patients with mixed DDD (i.e. dissociative amnesia+ Depersonalisation/ Derealisation) when calculating the prevalence rates. The median and interquartile range of age were reported if the original paper didn’t provide mean age (SD) or age range of the sample. bCDS = Cambridge Depersonalisation Scale; DDIS = Dissociative Disorders Interview Schedule; SCID-D = Structured Clinical Interview for DSM-IV Dissociative Disorders 22 J. YANG ET AL. unspecified or mixed disorders, the prevalence rates ranged from 4.4% (Mueller-Pfeiffer et al., 2012) to 41.9% (Sierra et al., 2006). In those patients with specific disorders, prevalence rates varied from 1.8% (Evren et al., 2007) to 53.8% (Somer et al., 2015). Compared with the review by Hunter et al. (2004), this review only included studies focusing on the prevalence rates of clinical DDD. One strength of the current study is that a review protocol was developed prior to beginning the literature search, and papers were screened based on the specific inclusion criteria. Additionally, only high or moderate quality papers using standardized assessment tools or scales with high reliability and validity were included. Around half of the studies used structured clinical interviews (e.g. DDIS, SCID-D) to diagnose the participants. It is worth noting that the overall prevalence rates of DDD were higher in studies diagnosing participants by self-report scales, which may lead to overestimation of DDD prevalence. The higher prevalence rate of 9.7% in Israel (Somer et al., 2015) could be due to some unique social causes in the Middle East, such as wars and conflicts (Pocock, 2017), which will cause traumatic experiences and stress that may increase the risk of DDD. Our findings show that DDD is more prevalent in the younger population, with a prevalence of around 11%, consistent with existing evidence that dissociative symptoms are more prevalent in adoles- cents (Carlson & Putnam, 1993). High levels of anxiety in the mid-teens (Abe & Suzuki, 1986) could be a potential factor when explaining the higher prevalence of DDD in the younger population, as existing literature suggests that depersonalization is associated with anxiety in the general population (Trueman, 1984). The prevalence of DDD in outpatient and inpatient samples propose that DDD is more common in patients with more severe mental health conditions. The wide range of prevalence rate of DDD in patients with other dissociative spectrum disorders may be accounted for by the variations in diagnostic mea- sures used; for example, Yayla et al. (2015) used the SCID-D while Mitchell et al. (2012) used the self-reported scale. In this case, the high prevalence of 20% in the study by Mitchell et al. (2012) could be caused by patient overestimation of their symptoms. The types of dissociation found in conversion disorder could be another possible factor for the low prevalence of DDD in patients with conver- sion disorder (Yayla et al., 2015). According to Holmes et al. (2005), detachment and compartmentalization (i.e. normally integrated cognitive or physical func- tions are disconnected) are two qualitatively different categories of dissociation. In this case, conversion disorder, which is characterized by compartmentaliza- tion, differs from DDD, which is characterized by detachment. There is consistent evidence that DDD is prevalent in those who have experienced interpersonal abuse. As the interpersonal abuse experience is unlikely to be the consequence of the DDD, one can speculate that interper- sonal abuse may be a risk factor for DDD. JOURNAL OF TRAUMA & DISSOCIATION 23 Table 3. Study characteristics of the studies involving patients with specific disorders. Authors & Prevalence Year of Mean age (SD) / Gender (% assessment Specific Disorders publication Country Population Patient type Sample size age range female) method Cut-off score Results from original papers Notes prevalence (%) Anxiety Disorders Panic disorder Mendoza Spain Adult patients Outpatients N = 104 M = 37.5; 71.1% (75) CDS 70 (≥70) n = 21 (20.2%) had a CDS 20.2% et al. with panic SD = 8.8 (Spanish version) score higher than 69 (2011) disorders (with during the panic attack, and without including 2 males and 19 agoraphobia) females Panic disorder Ural et al. Turkey Psychotropic Outpatients N = 92 M = 31.98; 63.0% (58) SCID-D (Turkish Meets DSM-IV n = 3 (3.3%) diagnosed with 3.3% (2015) drug-naïve SD = 7.32; version) criteria for depersonalisation adult patients range = 18–52 DDD diagnosis disorder according to with panic the SCID-D. disorder Social anxiety Belli et al. Turkey Psychotropic Outpatients N = 94 Not given 55.32% (52) SCID-D (Turkish Meets DSM-IV (1) n = 30 (31.91%) of the 94 **new 6.3% disorder (2017) drug-naïve - low version) criteria for patients were found to prevalence patients with Dissociation DDD diagnosis have dissociative = (5 + 1)/94 social anxiety Questionnaire disorder comorbidity = 6.3% disorder (SAD) score (< 2.5): (2) n = 5 (5.3%) patients n = 56 had depersonalisation - high disorder; Dissociation (3) One patient (1.0%) Questionnaire had dissociative amnesia score (>2.5): and depersonalisation, n = 38 (Continued) 24 J. YANG ET AL. Table 3. (Continued). Authors & Prevalence Year of Mean age (SD) / Gender (% assessment Specific Disorders publication Country Population Patient type Sample size age range female) method Cut-off score Results from original papers Notes prevalence (%) Anxiety Disorders Obsessive- Belli et al. Turkey Patients with Outpatients N = 78 M = 31.22; SD = 76.9% (60) SCID-D (Turkish Meets DSM-IV (1) n = 3 patients (3.84%) **new 10.26% compulsive (2012) obsessive- 8.83; range = version) criteria for were diagnosed as prevalence disorder compulsive 18–54 DDD diagnosis having with dissociative = (3 + 3 + 1 disorder (OCD) depersonalisation + 1)/78 disorder = 10.26% (2) 3 patients (3.84%) were diagnosed as having dissociative amnesia disorder + dissociative depersonalisation disorder; 1 patient (1.28%) was diagnosed as having dissociative depersonalisation disorder + dissociative identity disorder, and 1 patient (1.28%) was diagnosed as having dissociative amnesia disorder + dissociative depersonalisation disorder + dissociative identity disorder Dissociative spectrum disorders (Continued) JOURNAL OF TRAUMA & DISSOCIATION 25 Table 3. (Continued). Authors & Prevalence Year of Mean age (SD) / Gender (% assessment Specific Disorders publication Country Population Patient type Sample size age range female) method Cut-off score Results from original papers Notes prevalence (%) Anxiety Disorders Conversion disorder Yalya et al. Turkey Patients with Outpatients N = 54: - DD+: M = 28.05; 90.7% (49) SCID-D Meets DSM-IV n = 2 (3.7%) participants **in original 3.7% (2015) conversion -people SD = 7.54; criteria for had DDD paper, the disorder (CD) diagnosed - DD-: DDD diagnosis prevalence aged 18–65 with M = 29.21; was 3.7% in dissociative SD = 8.05 abstract but disorders (DD 1.08% in +): n = 20 result part. - people Correct without prevalence dissociative = 2/ disorders (DD- 54 = 3.7% ): n = 34 Non-epileptic attack Mitchell United Adult patients Not given N = 50: Total sample: 70% (35) Derealisation/ sub-score 20.4% of the sample **didn’t report 20.4% disorder et al. Kingdom with non- - NEAD only: M = 42.0; - NEAD Depersonalisation ≥30 reported pathological specific (2012) epileptic attack n = 39 SD = 14.5. only:69.2% subscale of DES levels of number disorder - dual - NEAD only: (27) depersonalisation and (NEAD) diagnosis: M = 41.6; - Dual derealisation symptoms n = 11 SD = 15.1 diagnosis: (sub-score≥30). - Dual 72.7% (8) diagnosis: M = 43.4; SD = 12.4 Substance use disorders Alcohol dependence Evren et al. Turkey Inpatients with Inpatients N = 111 M = 43.6; SD = 9.9; 5.4% (6) SCID-D (Turkish Meets DSM-IV (1) n = 1 (0.9%) patient **new 1.8% (2007) alcohol range = 18–68 version) criteria for diagnosed with prevalence = dependency DDD diagnosis a depersonalisation (1 + 1)/111 disorder. = 1.8% (2) 1 patient had amnesia and derealisation (Continued) 26 J. YANG ET AL. Table 3. (Continued). Authors & Prevalence Year of Mean age (SD) / Gender (% assessment Specific Disorders publication Country Population Patient type Sample size age range female) method Cut-off score Results from original papers Notes prevalence (%) Anxiety Disorders Opiate use disorder Somer Israel (1) patients with Inpatients N = 261 - Arab women: 59% (154) DDIS Meets DDIS (1) n = 43 (53.8%) Arab 5.9% et al. opiate use - Arab women: M = 33.29; - Arab criteria for women subjected to (2015) disorder n = 80; - OUD patients: women DDD diagnosis violence had DDD (2) Arab - OUD M = 32.44; group: (2) n = 4 (5.9%) opiate women patients: - Nonclinical: 100% (80) use disorder patients subjected to n = 68; M = 34.80 - OUD had DDD domestic - nonclinical: patient (3) n = 10 (9.7%) non- violence n = 103 group: clinical controls had DDD (3) Non-clinical 5.9% (4) controls from - a community Nonclinical sample Israeli (graduate group: 68% students and (70) their friends and family members) Interpersonal abuse (Continued) JOURNAL OF TRAUMA & DISSOCIATION 27 Table 3. (Continued). Authors & Prevalence Year of Mean age (SD) / Gender (% assessment Specific Disorders publication Country Population Patient type Sample size age range female) method Cut-off score Results from original papers Notes prevalence (%) Anxiety Disorders Domestic violence Somer Israel (1) Opiate use Inpatients N = 261 - Arab women: 59% (154) DDIS Meets DDIS (1)n = 43 (53.8%) Arab 53.8% et al. disorder - Arab women: M = 33.29; - Arab criteria for women subjected to (2015) patients n = 80; - OUD patients: women DDD diagnosis violence had DDD (2) Arab - OUD M = 32.44; group: (2) n = 4 (5.9%) opiate women patients: - Nonclinical: 100% (80) use disorder patients subjected to n = 68; M = 34.80 - OUD had DDD domestic - nonclinical: patient (3) n = 10 (9.7%) non- violence n = 103 group: clinical controls had DDD (3) Non-clinical 5.9% (4) controls from - a community nonclinical sample Israeli (graduate group: 68% students and (70) their friends and family members) Interpersonal abuse Aponte- Puerto Rico Hispanic adults participants 80 M = 31.00; 65% (52) CDS (Spanish 70 (>70) (1)25% of HIA group scored **didn’t report 25% Soto with and from - HIA: n = 40 SD = 9.9; - HIA: 65% version) > 70 on CDS specific et al. without mental - CCG: n = 40 range = 21–65 (26) (2) No participants number (2019) a history of health - CCG: 65% scored >70 on CDS in interpersonal clinics (26) the CCG group abuse - participants with a history of interpersonal abuse (HIA); - control community group (CCG) without HIA Other specific disorders (Continued) 28 J. YANG ET AL. Table 3. (Continued). Authors & Prevalence Year of Mean age (SD) / Gender (% assessment Specific Disorders publication Country Population Patient type Sample size age range female) method Cut-off score Results from original papers Notes prevalence (%) Anxiety Disorders Depression Zikic et al. Serbia Patients suffering inpatients and N = 84 DP group: 76.2% (64) CDS 70(≥70) n = 40 (47.6%) subjects 47.6% (2009) from unipolar outpatients M = 44.5; scored higher or equal to depression low DP group 70, including 8 males without (scored lower (20%) and 32 females psychotic than 70): (80%) features aged M = 45.7 18–65 Schizophrenia or Gonzalez- Spain (1) Patients with inpatients N = 392: Overall: Not given CDS (Spanish version) 71 (1) Among 141 patients, ** errors in 16.3% in patients schizophrenia Torres schizophrenia - n = 147 Median = 30.0, n = 24 (17%) had DDD calculation with spectrum et al. or patients; interquartile according to the cut-off in original schizophrenia disorders (2010) schizophrenia - n = 73 first- range = 24–42 point of 71. paper. or spectrum degree - Patients: (2) Among 71 relatives, Correct schizophrenia disorders relatives; Median = 32, n = 1 (1%) had DDD prevalence spectrum (2) First-degree - n = 172 interquartile according to the cut-off were: disorders; healthy control range = 25–40 point of 71. (1) patients: 1% in relatives relatives with subjects - Relatives: (3) Among 172 controls, 24/ of patients; no psychiatric Median = 35.5, n = 2 (3%) had DDD 147 = 16.3% history interquartile according to the cut-off (3) controls: (3) Healthy range = 28– point of 71. 2/ controls from 43.3 172 = 1.16%. the general - Controls: population Median = 27, interquartile range = 23– 40.3 Borderline Korzekwa Canada Adult patients outpatients N = 21 M = 38; SD = 8 76% SCID-D Meets DSM-IV n = 4 (19%) patients with 19% personality et al. with **54 eligible * for N = 21 criteria for BPD had DDD according disorder (2009) borderline patients (BPD) DDD diagnosis to SCID-D-R personality but only 21 disorder (BPD) patients completed the SCID-D-R aWe recalculated the prevalence rates of DDD for all included papers. When the original papers had calculation errors in prevalence rates, we reported the correct prevalence rates in the results. We included patients with mixed DDD (i.e. dissociative amnesia+ Depersonalisation/ Derealisation) when calculating the prevalence rates. The median and interquartile range of age were reported if the original paper didn’t provide mean age (SD) or age range of the sample. bCDS = Cambridge Depersonalisation Scale; DES = Dissociation Experiences Scale; DDIS = Dissociative Disorders Interview Schedule; SCID-D = Structured Clinical Interview for DSM-IV Dissociative Disorders. JOURNAL OF TRAUMA & DISSOCIATION 29 The high prevalence of DDD in depressive patients should be interpreted carefully, as Žikić et al. (2009) assessed DDD prevalence using the CDS and some of these items overlap with depressive symptoms, which may lead to overestimation of DDD. Additionally, the findings amongst people with sub- stance use should be treated with caution, as drug use could trigger experi- ences of depersonalization and derealization (Madden & Einhorn, 2018) and drug-induced depersonalization is similar to non-drug-induced depersonali- zation (Medford et al., 2003). Clinical & empirical relevance The finding that DDD is more prevalent in patients with other mental disorders and patients with more severe mental health conditions echo hypotheses by Mula et al. (2007) that depersonalization may represent an index of disease severity. However, DDD is severely neglected in clinical settings as clinicians are unfamiliar with its features and treatment and a misdiagnosis could be made due to the overlap between DDD and depres- sion (Michal et al., 2016). Clinicians should be aware of the possibility of DDD when diagnosing patients and consider the influence of comorbidity when treating patients. For instance, depersonalization is related to treatment resis- tance in anxiety disorders and depression (Mula et al., 2007). Beyond this, there is a severe dearth of effective treatments for DDD as a primary or secondary diagnosis. Interventions specifically aimed at DDD and evidence of treatment effectiveness are needed. Moreover, although the existing litera- ture indicates that DDD has a high comorbidity with anxiety disorders and depression (Michal et al., 2016), limited studies focus on the presence of DDD in patients already diagnosed with other mental disorders and how DDD may interact with these other disorders, affecting the severity of symptoms, response to treatment and prognosis. Limitations & future directions This review has some limitations. Firstly, we did not measure publication bias. As negative findings, (i.e. studies that did not detect participants diagnosed with DDD) are less likely to be published, the prevalence of DDD could be over- estimated. Secondly, considering the high heterogeneity of included studies (i.e. the variability of the study population), we did not conduct a meta-analysis. The small number of included studies is another limitation. For instance, we only found one paper involving patients with depression, thus the results could be unrepresentative. Beyond this, although we have assessed the quality of the included papers, the potential selection bias and response bias still existed. Specifically, according to the quality assessment results, almost half of the included studies were at risk of response bias. In addition, all of the included 30 J. YANG ET AL. Table 4. The specific prevalence assessment tools and the results (prevalence rates) in studies using self-reported scales and diagnostic interviews. Prevalence assessment tools Authors (year of publication) Prevalence (%) Studies using self-reported scales Cambridge Depersonalisation Sierra et al. (2006) 41.9% in UK inpatients;35.8% in Spain Scale inpatients; 17.5% in Colombia inpatients Zikic et al. (2009) 47.6% Myers & Llera (2020) 11% Aponte-Soto et al. (2019) 25% in participants with a history of interpersonal abuse; 0% in control group Cambridge Depersonalisation Gonzalez-Torres et al. (2010) 16.3% in patients with schizophrenia or Scale (Spanish version) schizophrenia spectrum disorders; 1% in relatives of patients; 1.16% in healthy control Mendoza et al. (2011) 20.2% 2-item Cambridge Michal, Wiltink, Till, Wild, 0.8% Depersonalisation Scale (CDS- Blettner, et al., 2010. (2010) 2) Michal et al. (2015) 11.9% Schlax et al. (2020) 0.76% 9-item Cambridge Michal et al. (2009) 1.9% Depersonalisation Scale (CDS- 9) Derealisation/Depersonalisation Mitchell et al. (2012) 20.4% subscale of Dissociation Experiences Scale (DES) Studies using diagnostic interviews Dissociative Disorders Interview Garcia et al. (2006) 6% Schedule (DDIS) Dorahy et al. (2006) 10% Foote et al. (2006) 5% Somer et al. (2015) 53.8% in Arab women 5.9% in OUD patients 9.7% in the nonclinical group Structured Clinical Interview for Mueller-Pfeiffer et al. (2012) 4.4% DSM-IV Dissociative Disorders Korzekwa et al. (2009) 19% (SCID-D) Belli et al. (2012) 3.84% Johnson et al. (2006) 0.8% Yalya et al. (2015) 3.7% Ural et al. (2015) 3.3% SCID-D (Turkish version) Evren et al. (2007) 0.9% Belli et al. (2017) 5.3% studies were published in English and there was a lack of studies from Australia, Southeast Asia, Central America, and African countries. Future research could focus on the prevalence of DDD in those settings and explore whether different cultural backgrounds have an impact. It should be noted that our review only provided descriptive epidemiological information about the frequency of DDD. Therefore, although we establish an association between DDD and potential risk factors, we still cannot infer any causal relationships between them. Conclusion This review summarizes the results of epidemiological studies, providing an update to our knowledge of the prevalence of DDD amongst different popula- tions. The included studies were from a range of countries, allowing for a broader understanding of the prevalence rate of DDD across the globe. Overall, results JOURNAL OF TRAUMA & DISSOCIATION 31 indicate that the prevalence rate of DDD ranges from 1% to 2% in the general population, remaining consistent with previous findings (Hunter et al., 2004). We also find a trend that DDD is more prevalent amongst adolescents and young adults. Although the prevalence rates amongst patients with unspecified or specific disorders varies, it remains consistent that DDD is more prevalent in patients with mental health conditions than in the general population, suggesting that patients who already have other diagnoses are more vulnerable to DDD. Disclosure statement No potential competing interest was reported by the authors. Funding The author(s) reported there is no funding associated with the work featured in this article. ORCID Jinyan Yang http://orcid.org/0000-0003-4526-7385 L. S. Merritt Millman http://orcid.org/0000-0002-7872-0679 Anthony S. David http://orcid.org/0000-0003-0967-774X Elaine C.M. Hunter http://orcid.org/0000-0002-6479-2954 References Abe, K., & Suzuki, T. (1986). Prevalence of some symptoms in adolescence and maturity: social phobias, anxiety symptoms, episodic illusions and idea of reference. Psychopathology, 19(4), 200–205. https://doi.org/10.1159/000284448 American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). https://doi.org/10.1176/appi.books.9780890425596 Aponte-Soto, M., Martinez-Taboas, A., Vélez-Pastrana, M. C., & González, R. A. (2019). The relationship between interpersonal abuse and depersonalization experiences. Revista Puertorriqueña de Psicología, 30(1), 48–59. https://www.researchgate.net/publication/ 334455133 Baker, D., Hunter, E., Lawrence, E., Medford, N., Patel, M., Senior, C., Sierra, M., Lambert, M. V., Phillips, M. L., & David, A. S. (2003). Depersonalisation disorder: Clinical features of 204 cases. The British Journal of Psychiatry, 182(5), 428–433. https://doi.org/10.1192/bjp.182.5.428 Belli, H., Ural, C., Vardar, M. K., Yesılyurt, S., & Oncu, F. (2012). Dissociative symptoms and dissociative disorder comorbidity in patients with obsessive-compulsive disorder. Comprehensive Psychiatry, 53(7), 975–980. https://doi.org/10.1016/j.comppsych.2012.02.004 Belli, H., Akbudak, M., Ural, C., Solmaz, M., Dogan, Z., & Konkan, R. (2017). Is there a complex relation between social anxiety disorder, childhood traumatic experiences and dissociation? Nordic Journal of Psychiatry, 71(1), 55–60. https://doi.org/10.1080/08039488. 2016.1218050 32 J. YANG ET AL. Bernstein, E. M., & Putnam, F. W. (1986). Development, reliability, and validity of a dissociation scale. The Journal of Nervous and Mental Disease, 174(12), 727–735. https:// doi.org/10.1097/00005053-198612000-00004 Carlson, E. B., & Putnam, F. W. (1993). An update on the dissociative experiences scale. Dissociation: Progress in the Dissociative Disorders, 6(1), 16–27. https://www.researchgate. net/publication/232515683_An_Update_on_the_Dissociative_Experiences_Scale . Dorahy, M. J., Mills, H., Taggart, C., O’Kane, M., & Mulholland, C. (2006). Do dissociative disorders exist in Northern Ireland?: Blind psychiatric-structured interview assessments of 20 complex psychiatric patients. The European Journal of Psychiatry, 20(3), 172–182. https:// doi.org/10.4321/S0213-61632006000300005 Duffy, C. M. (2000). Prevalence of undiagnosed dissociative disorders in an inpatient setting. ProQuest Dissertations Publishing. Evren, C., Sar, V., Karadag, F., Tamar Gurol, D., & Karagoz, M. (2007). Dissociative disorders among alcohol-dependent inpatients. Psychiatry Research, 152(2), 233–241. https://doi.org/ 10.1016/j.psychres.2005.08.004 Foote, B., Smolin, Y., Kaplan, M., Legatt, M. E., & Lipschitz, D. (2006). Prevalence of Dissociative Disorders in Psychiatric Outpatients. American Journal of Psychiatry, 163(4), 623–629. https://doi.org/10.1176/ajp.2006.163.4.623 Foote, B., Smolin, Y., Neft, D. I., & Lipschitz, D. (2008). Dissociative disorders and suicidality in psychiatric outpatients. The Journal of Nervous and Mental Disease, 196(1), 29–36. https:// doi.org/10.1097/nmd.0b013e31815fa4e7 García, R. R., Rico, S. E. G., & Agráz, F. P. (2006). Disociative disorders in Mexican psychiatric patients: Prevalence, comorbidity and dissociative experiences scale psychometric properties. Salud Mental, 29(2), 38–43. https://www.medigraphic.com/cgi-bin/new/ resumenI.cgi?IDARTICULO=13954 . Gonzalez-Torres, M. A., Inchausti, L., Aristegui, M., Ibañez, B., Diez, L., Fernandez-Rivas, A., Bustamante, S., Haidar, K., Rodríguez-Zabaleta, M., & Mingo, A. (2010). Depersonalization in patients with schizophrenia spectrum disorders, first-degree relatives and normal controls. Psychopathology, 43(3), 141–149. https://doi.org/10.1159/000288635 Higgins, J. J. N.-S. A. F. E. P. U. P. (2008). Cochrane handbook for systematic reviews of interventions version 5.0.1. The Cochrane Collaboration, 5(2), S38. www.training.cochrane. org/handbook . Higgins J. P. T., Thomas, J., Chandler, J., Cumpston, M., Li, T., Page, M. J., Welch, VA (editors). 2022. Cochrane Handbook for Systematic Reviews of Interventions version 6.3 (updated February 2022). Cochrane. Available from www.training.cochrane.org/handbook . Holmes, E. A., Brown, R. J., Mansell, W., Fearon, R. P., Hunter, E. C. M., Frasquilho, F., & Oakley, D. A. (2005). Are there two qualitatively distinct forms of dissociation? A review and some clinical implications. Clinical Psychology Review, 25(1), 1–23. https://doi.org/10.1016/j. cpr.2004.08.006 Hoy, D., Brooks, P., Woolf, A., Blyth, F., March, L., Bain, C., Baker, P., Smith, E., & Buchbinder, R. (2012). Assessing risk of bias in prevalence studies: Modification of an existing tool and evidence of interrater agreement. Journal of Clinical Epidemiology, 65(9), 934–939. https://doi.org/10.1016/j.jclinepi.2011.11.014 Hunter, C., Sierra, E., David, M., A, S. J. S. P., & Epidemiology, P. (2004). The epidemiology of depersonalisation and derealisation: A systematic review. Public Health Nutrition, 7(2), 337–343. https://doi.org/10.1079/PHN2003526 Johnson, J., Cohen, P., Kasen, S., & Brook, J. (2006). Dissociative disorders among adults in the community, impaired functioning, and axis I and II comorbidity. Journal of Psychiatric Research, 40(2), 131–140. https://doi.org/10.1016/j.jpsychires.2005.03.003 JOURNAL OF TRAUMA & DISSOCIATION 33 Korzekwa, M. I., Dell, P. F., Links, P. S., Thabane, L., & Fougere, P. (2009). Dissociation in borderline personality disorder: A detailed look. Journal of Trauma & Dissociation, 10(3), 346–367. https://doi.org/10.1080/15299730902956838 Madden, S. P., & Einhorn, P. M. (2018). Cannabis-induced depersonalization-derealization disorder The American Journal of Psychiatry Residents’ Journal, 13(2), 3–6. https://doi.org/ 10.1176/appi.ajp-rj.2018.130202 Maslach, C., & Jackson, S. E. (1981). The measurement of experienced burnout. Journal of Organizational Behavior, 2(2), 99–113. https://doi.org/10.1002/job.4030020205 Medford, N., Baker, D., Hunter, E., Sierra, M., Lawrence, E., Phillips, M. L., & David, A. S. (2003). Chronic depersonalization following illicit drug use: A controlled analysis of 40 cases. Addiction (Abingdon, England), 98(12), 1731–1736. https://doi.org/10.1111/j.1360-0443.2003.00548.x Mendoza, L., Navinés, R., Crippa, J. A., Fagundo, A. B., Gutierrez, F., Nardi, A. E., Bulbena, A., Valdés, M., & Martín-Santos, R. (2011). Depersonalization and personality in panic disorder. Comprehensive Psychiatry, 52(4), 413–419. https://doi.org/10.1016/j.comppsych.2010.09.002 Michal, M., Sann, U., Niebecker, M., Lazanowsky, C., Kernhof, K., Aurich, S., Overbeck, G., Sierra, M., & Berrios, G. E. (2004). Die erfassung des depersonalisations-derealisations- syndroms mit der deutschen version der Cambridge Depersonalisation Scale (CDS). PPmP- Psychotherapie· Psychosomatik· Medizinische Psychologie, 54(9/10), 367–374. https://doi.org/10. 1055/s-2004-828296 Michal, M., Wiltink, J., Subic-Wrana, C., Zwerenz, R., Tuin, I., Lichy, M., Brähler, E., & Beutel, M. E. (2009). Prevalence, Correlates, and Predictors of Depersonalization Experiences in the German General Population. The Journal of Nervous and Mental Disease, 197(7), 499–506. https://doi.org/10.1097/nmd.0b013e3181aacd94 Michal, M., Wiltink, J., Till, Y., Wild, P. S., Blettner, M., & Beutel, M. E. (2010). Distinctiveness and overlap of depersonalization with anxiety and depression in a community sample: Results from the Gutenberg heart study. Psychiatry Research, 188(2), 264–268. https://doi. org/10.1016/j.psychres.2010.11.004 Michal, M., Zwerenz, R., Tschan, R., Edinger, J., Lichy, M., Knebel, A., Tuin, I., & Beutel, M. (2010). Screening nach depersonalisation-derealisation mittels zweier items der Cambridge depersonalisation scale. PPmP-Psychotherapie· Psychosomatik· Medizinische Psychologie, 60 (5), 175–179. https://doi.org/10.1055/s-0029-1224098 Michal, M., Wiltink, J., Till, Y., Wild, P. S., Münzel, T., Blankenberg, S., & Beutel, M. E. (2010). Type-D personality and depersonalization are associated with suicidal ideation in the German general population aged 35–74: Results from the Gutenberg heart study. Journal of Affective Disorders, 125(1–3), 227–233. https://doi.org/10.1016/j.jad.2010.02.108 Michal, M., Duven, E., Giralt, S., Dreier, M., Müller, K. W., Adler, J., Beutel, M. E., & Wölfling, K. (2015). Prevalence and correlates of depersonalization in students aged 12–18 years in Germany. Social Psychiatry and Psychiatric Epidemiology, 50(6), 995–1003. https:// doi.org/10.1007/s00127-014-0957-2 Michal, M., Adler, J., Wiltink, J., Reiner, I., Tschan, R., W?lfling, K., and Beutel, M. E. J. B. P. (2016). A case series of 223 patients with depersonalization-derealization syndrome. BMC Psychiatry, 16 (1). https://bmcpsychiatry.biomedcentral.com/articles/10.1186/s12888-016-0908-4 Mitchell, J. W., Ali, F., & Cavanna, A. E. (2012). Dissociative experiences and quality of life in patients with non-epileptic attack disorder. Epilepsy and Behavior, 25(3), 307–312. https:// doi.org/10.1016/j.yebeh.2012.08.022 Mueller-Pfeiffer, C., Rufibach, K., Perron, N., Wyss, D., Kuenzler, C., Prezewowsky, C., Pitman, R. K., & Rufer, M. (2012). Global functioning and disability in dissociative disorders. Psychiatry Research, 200(2), 475–481. https://doi.org/10.1016/j.psychres.2012.04. 028 34 J. YANG ET AL. Mula, M., Pini, S., & Cassano, G. B. J. J. A. D. (2007). The neurobiology and clinical significance of depersonalization in mood and anxiety disorders: A critical reappraisal. Journal of Affective Disorders, 99(1–3), 91–99. https://doi.org/10.1016/j.jad.2006.08.025 Myers, N. S., & Llera, S. J. (2020). The role of childhood maltreatment in the relationship between social anxiety and dissociation: A novel link. Journal of Trauma & Dissociation, 21 (3), 319–336. https://doi.org/10.1080/15299732.2020.1719265 Nguyen, K. A., Peer, N., Mills, E. J., Kengne, A. P., & Menéndez-Arias, L. (2016). A meta-analysis of the metabolic syndrome prevalence in the global HIV-infected population. PloS One, 11(3), e0150970. https://doi.org/10.1371/journal.pone.0150970 Pocock, L. (2017). Mental health issues in the Middle East: An overview. Middle East Journal of Psychiatry and Alzheimers, 8(1), 10–15. https://doi.org/10.5742/MEPA.2017.93004 Ross, C. A., Heber, S., Norton, G. R., Anderson, D., Anderson, G., & Barchet, P. (1989). The dissociative disorders interview schedule: A structured interview. Dissociation, 2(3), 169– 189. http://hdl.handle.net/1794/1505 . Schlax, J., Wiltink, J., Beutel, M. E., Münzel, T., Pfeiffer, N., Wild, P., Blettner, M., Ghaemi Kerahrodi, J., & Michal, M. (2020). Symptoms of depersonalization/derealization are inde- pendent risk factors for the development or persistence of psychological distress in the general population: Results from the Gutenberg health study. Journal of Affective Disorders, 273, 41–47. https://doi.org/10.1016/j.jad.2020.04.018 Sierra, M., & Berrios, G. E. (2000). The Cambridge Depersonalisation Scale: A new instrument for the measurement of depersonalisation. Psychiatry Research, 93(2), 153–164. https://doi. org/10.1016/S0165-1781(00)00100-1 Sierra, M., Gomez, J., Molina, J. J., Luque, R., Muñoz, J. F., & David, A. S. (2006). Depersonalization in Psychiatric Patients: A Transcultural Study. The Journal of Nervous and Mental Disease, 194(5), 356–361. https://doi.org/10.1097/01.nmd.0000218071.32072.74 Simeon, D., Guralnik, O., Gross, S., Stein, D. J., Schmeidler, J., & Hollander, E. (1998). The detection and measurement of depersonalization disorder. The Journal of Nervous and Mental Disease, 186(9), 536–542. https://doi.org/10.1097/00005053-199809000-00004 Somer, E., Ross, C., Kirshberg, R., Bakri, R. S., & Ismail, S. (2015). Dissociative disorders and possession experiences in Israel: A comparison of opiate use disorder patients, Arab women subjected to domestic violence, and a nonclinical group. Transcultural Psychiatry, 52(1), 58–73. https://doi.org/10.1177/1363461514552584 Steinberg, M. (1994). Interviewer’s guide to the structured clinical interview for DSM-IV dissociative disorders. American Psychiatric Pub. Trueman, D. (1984). Anxiety and depersonalization and derealization experiences. Psychological Reports, 54(1), 91–96. https://doi.org/10.2466/pr0.1984.54.1.91 Tschan, R., Wiltink, J., Adler, J., Beutel, M. E., & Michal, M. (2013). Depersonalization experiences are strongly associated with dizziness and vertigo symptoms leading to increased health care consumption in the German general population. The Journal of Nervous and Mental Disease, 201(7), 629–635. https://doi.org/10.1097/NMD. 0b013e3182982995 Ural, C., Belli, H., Akbudak, M., & Tabo, A. (2015). Childhood traumatic experiences, dis- sociative symptoms, and dissociative disorder comorbidity among patients with panic disorder: A preliminary study. Journal of Trauma & Dissociation, 16(4), 463–475. 10.1080/ 15299732.2015.1019175 Waller, N. G., Putnam, F. W., & Carlson, E. B. (1996). Types of dissociation and dissociative types: A taxometric analysis of dissociative experiences. Psychological Methods, 1(3), 300–321. 10.1037/1082-989X.1.3.300 JOURNAL OF TRAUMA & DISSOCIATION 35 Yayla, S., Bakım, B., Tankaya, O., Ozer, O. A., Karamustafalioglu, O., Ertekin, H., & Tekin, A. (2015). Psychiatric comorbidity in patients with conversion disorder and prevalence of dissociative symptoms. Journal of Trauma & Dissociation, 16(1), 29–38. 10.1080/ 15299732.2014.938214 Žikić, O., Ćirić, S., & Mitković, M. (2009). Depressive phenomenology in regard to deperso- nalization level. Psychiatria Danubina, 21(3), 320–326. https://www.researchgate.net/publi cation/26860962_Depressive_phenomenology_in_regard_to_depersonalization_level Appendix Appendix 1: Systematic review protocol in PROSPERO format Review Title The prevalence of depersonalization and derealization (DP/DR) disorders: a systematic review Review question What are the prevalence rates of DP/DR disorders in different population (e.g. non-clinical population, patients with mixed or unspecified disorders, and patients within specific disorders)? Searches Databases The following databases will be searched and reviewed: MEDLINE PsycINFO Web of science. These databases will be combined and searched. Grey literature will also be searched in Google Search to ensure that other relevant literature not retrieved in electronic databases can be covered. Before the final analysis, the search process will be repeated to include new published literature and avoid any potential mistakes in first search. Search terms Concept 1: depersonalization OR derealization OR depersonalisation OR derealisation OR Depersonalization/Derealization Disorder OR Depersonalisation disorder OR Depersonalization Disorder OR derealization disorder OR derealisation disorder Concept 2: epidemiolog* OR prevalen* OR occurrence OR frequency Both UK and US spellings will be searched. Within each concept, the Boolean operator “OR” will be used to group all the search terms within the corresponding concept, and the Boolean operator “AND” will be used to combine two concepts. Limitation All searches will be limited to humans and English language. The results will be limited to studies published after October 2002. The deduplication process will be conducted after finishing the search. Types of study to be included We will only include quantitative studies that provide prevalence rates of DP/DR disorders or provide information to calculate prevalence rates. Reviews will be excluded but the reference lists of reviews will be manually checked to retrieve relevant studies. Condition or domain being studied Inclusion: Eligible studies must focus on the prevalence rate of DP/DR disorders, which is defined by structured clinical interviews using DSM-IV, DSM-V or ICD-10 criteria, such as the Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID-D; Steinberg, 1994) and the Dissociative Disorders Interview Schedule (DDIS; Ross et al., 1989). Additionally, 36 J. YANG ET AL. studies that used Cambridge Depersonalisation Scale (CDS; Sierra &Berrios, 2000) and taxon version of Dissociation Experiences Scale (DES; Bernstein and Putnam, 1986) and provided clinical cut-off scores (70 for CDS and 13 for taxon DES) will also be included. Studies using the 2-item version CDS (CDS-2; Sierra and Berrios, 2000; Michal, Wiltink, Till, Wild, Blettner, et al., 2010) with a cut-off of 3 and the 9-item version CDS with a cut-off of 19 (CDS-9; Sierra and Berrios, 2000; Michal et al., 2004) are also accepted. The outcome of eligible studies should include the prevalence rate of DP/DR disorders. Exclusion: Studies that focus on the relationship between DP/DR disorders and risk factors will be excluded. Studies that only provide prevalence rates of other mental disorders will be excluded. Studies that only give prevalence of symptoms of DP/DR without a standardized measures and clinical cut-off will be excluded. Studies that focus on burnout or burnout syndrome will also be excluded. Participants/population Inclusion: Both clinical and non-clinical population will be included. Exclusion: N/A Intervention(s) N/A Comparator(s)/control N/A Context Geographical locations are not limited. Main outcome(s) The main outcome is the prevalence rates of DP/DR disorders. Studies that do not provide prevalence or the information that can be used to calculate prevalence will be excluded. For studies that only provide information to calculate prevalence rates, prevalence will be calcu- lated by dividing the number of people identified as having DP/DR disorders by the total sample size. Secondary outcome(s) None. Data extraction (selection and coding) The search results will be deduplicated, downloaded and imported to Endnote 7 for storing and screening. Two independent reviewers will screen the titles and abstracts of the identified papers against the pre-specified criteria. Reviewers will record the titles of the excluded studies and reasons of excluding them. Then, these reviewers will retrieve the full texts of the remained studies and assess their eligibility using the criteria. The disagreements about inclusion will be resolved by discussion with a third reviewer. Data extraction will be conducted by the reviewers using a standardized form, which is adapted from Cochrane Data collection form template (Higgins et al., 2022). Extracted information included authors, year of publication, country, study population, sample size, mean age (SD) or age range of the study sample, prevalence assessment methods and cut-off score, and relevant results of the study (prevalence rates of DDD). Any discrepancies between two reviewers will be resolved through discussion with a third reviewer. Risk of bias (quality) assessment To assess the quality of prevalence studies, Quality assessment checklist for prevalence studies (adapted from Hoy et al.) will be used. The checklist includes nine domains (items 1 to 9) and the scores of these items will be combined to generate an overall score to provide an overall assessment of the study quality (item 10). In each domain, reviewer will provide information about whether the risk of bias is low or high. A score of zero in each item indicates low risk in corresponding domain, while a score of one indicates high risk. A low overall risk JOURNAL OF TRAUMA & DISSOCIATION 37 will be indicated by an overall score between zero to three, while a high overall risk will be indicated by an overall score between seven to nine. An overall score between four to six indicates a moderate overall risk of the study. An intraclass correlation coefficient will be calculated to indicate the inter-rater reliability of risk of bias assessment results. Any disagreement between reviewers will be resolved by a discussion with a third reviewer. The final result of risk of bias will be presented in an independent table. Strategy for data synthesis We will conduct a narrative analysis to provide findings from selected studies. The study population characteristics (e.g. age, sample size, gender), settings, prevalence assessment methods and prevalence rates will be synthesized. Analysis of subgroups or subsets Subgroup analysis will be conducted to explore the prevalence rates among non-clinical population, clinical population with unspecified or mixed disorders and clinical population within specific disorders. Type and method of review Systematic review Anticipated or actual start date 15/03/2020 Anticipated completion date 01/08/2020 Funding sources/sponsors University College London, Division of Psychiatry Conflicts of interest None known Language English Country England Stage of review Review completed Appendix 2: Original search history Database: APA PsycInfo <1806 to March Week 4 2020> Search Strategy: – – – – – – – – – – – – – – – – – – – – – – – – – – – 1 (depersonalization or derealization or depersonalisation or derealisation or Depersonalisation disorder or Depersonalization Disorder or derealization disorder or derea- lisation disorder).mp. [mp = title, abstract, heading word, table of contents, key concepts, original title, tests & measures, mesh] (4368) 2 exp Depersonalization/ or exp “Depersonalization/Derealization Disorder”/ (933) 3 1 or 2 (4368) 4 (epidemiolog* or prevalen* or occurrence or frequency).mp. [mp = title, abstract, heading word, table of contents, key concepts, original title, tests & measures, mesh] (409,186) 5 3 and 4 (596) 6 limit 5 to (human and English language and yr = “2002 – Current”) (348) *************************** Database: Ovid MEDLINE (R) <1946 to March Week 3 2020> 38 J. YANG ET AL. Search Strategy: – – – – – – – – – – – – – – – – – – – – – – – – – – – 1 (depersonalization or derealization or depersonalisation or derealisation or Depersonalisation disorder or Depersonalization Disorder or derealization disorder or derea- lisation disorder).mp. [mp = title, abstract, original title, name of substance word, subject heading word, floating sub-heading word, keyword heading word, organism supplementary concept word, protocol supplementary concept word, rare disease supplementary concept word, unique identifier, synonyms] (3020) 2 Depersonalization/ (1547) 3 1 or 2 (3020) 4 (epidemiolog* or prevalen* or occurrence or frequency).mp. [mp = title, abstract, original title, name of substance word, subject heading word, floating sub-heading word, keyword heading word, organism supplementary concept word, protocol supplementary concept word, rare disease supplementary concept word, unique identifier, synonyms] (2,912,240) 5 3 and 4 (971) 6 limit 5 to (English language and humans and yr = “2002–Current”) (664) *************************** Web of Science core collection Search History Combine Delete Sets Sets Edit AND OR Select Set Results Save History/Create AlertOpen Saved History Sets Combine AllDelete # 3 774 #2 AND #1 Edit Indexes = SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC Timespan = 2002–2020 # 2 3,769 TS = (depersonalization OR derealization OR depersonalisation OR Edit derealisation OR Depersonalization/Derealization Disorder OR Depersonalisation disorder OR Depersonalization Disorder OR derealization disorder OR derealisation disorder) Indexes = SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC Timespan = All years # 1 3,974,514 TS = (epidemiolog* OR prevalen* OR occurrence OR frequency) Edit Indexes = SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC Timespan = All years JOURNAL OF TRAUMA & DISSOCIATION 39 Appendix 3: Quality assessment tool (Hoy et al., 2012; Nguyen et al.,2016) 40 J. YANG ET AL. Appendix 4: Results of quality assessment Table A1. Results of quality assessment (risk of bias) of 22 included papers. 1. Was the study’s target population 7. Was the study 8. Was the 9. Were the a close 2. Was the 3. Was some 5. Were data instrument that same numerator (s) representation of sampling form of random 4. Was the collected 6. Was an measured the mode of and Summary the national frame a true or selection used to likelihood directly acceptable parameter of interest data denominator(s) score on population in close select the of non- from the case (e.g. prevalence of low collection for the the relation to relevant representation sample, OR, was response subjects (as definition back pain) shown to used for parameter of overall Year of variables, e.g. age, of the target a census bias opposed to used in the have reliability and all interest risk of Authors publication sex, occupation? population? undertaken? minimal? a proxy)? study? validity (if necessary)? subjects? appropriate? study bias Ural et al. 2015 1 0 0 0 0 1 0 0 0 2 Mendoza 2011 1 0 1 1 0 0 0 0 0 3 et al. Gonzalez- 2010 1 1 1 1 0 0 0 0 1 5 Torres et al. Sierra 2006 1 0 1 1 0 0 0 0 0 3 et al. Zikic et al. 2009 1 1 0 0 0 1 0 0 0 3 Garcia 2006 1 1 1 0 0 1 0 0 0 4 et al. Korzekwa 2009 1 0 0 0 0 1 0 0 0 2 et al. Johnson 2006 1 0 0 1 0 1 0 0 1 4 et al. Evren 2007 1 0 0 0 0 1 0 0 0 2 et al. Somer 2015 1 0 1 1 0 1 0 0 1 5 et al. Mitchell 2012 1 0 0 0 0 1 0 0 1 3 et al. Belli et al. 2012 1 0 0 0 0 1 0 0 0 2 Michal 2010 1 0 0 1 0 1 0 0 0 3 et al. Dorahy 2006 1 1 1 0 0 1 0 0 0 4 et al. (Continued) JOURNAL OF TRAUMA & DISSOCIATION 41 Table A1. (Continued). 1. Was the study’s target population 7. Was the study 8. Was the 9. Were the a close 2. Was the 3. Was some 5. Were data instrument that same numerator (s) representation of sampling form of random 4. Was the collected 6. Was an measured the mode of and Summary the national frame a true or selection used to likelihood directly acceptable parameter of interest data denominator(s) score on population in close select the of non- from the case (e.g. prevalence of low collection for the the relation to relevant representation sample, OR, was response subjects (as definition back pain) shown to used for parameter of overall Year of variables, e.g. age, of the target a census bias opposed to used in the have reliability and all interest risk of Authors publication sex, occupation? population? undertaken? minimal? a proxy)? study? validity (if necessary)? subjects? appropriate? study bias Mueller- 2012 1 0 0 0 0 0 0 0 0 1 Pfeiffer et al. Belli et al. 2017 1 0 0 0 0 1 0 0 0 2 Michal 2015 1 0 0 0 0 0 0 0 0 1 et al. Foote 2006 1 0 0 0 0 1 0 0 0 2 et al. Michal 2009 0 0 0 1 0 0 0 0 0 1 et al. Yalya 2015 1 0 1 1 0 1 0 0 0 4 et al. Aponte- 2019 1 0 1 1 0 0 0 0 1 4 Soto et al. Myers & 2020 1 1 1 1 0 1 0 0 0 5 Llera Schlax 2020 1 0 0 0 0 0 0 0 0 1 et al. a Low risk of bias: overall score of 0-3; Moderate risk of bias: overall score of 4-6; High risk of bias: overall score of 7-9 a Low risk of bias: overall score of 0–3; Moderate risk of bias: overall score of 4–6; High risk of bias: overall score of 7–9