The search strategy resulted in 9931 articles. Following title/abstract screening, 323 studies were retained for full-text review, resulting in 93 included articles (see Figure 1). A description of these studies is available in Supplementary Table S2 and effect sizes for individual studies included in the positive symptom, negative symptom, and disorganization analyses are presented in Supplementary Table S3.
The eligible studies comprised a total of 20 436 participants. Of these, 11 791 were women and 7627 were men, with a mean age of 27.07 years. Six studies did not specify gender and 19 did not specify age. In total, 58 presented data from nonclinical populations (n = 16 557) and 46 from patient groups (n = 3879).
Results of the EPHHP quality ratings are presented in Supplementary Table S2. Most studies fell within the "moderate" rating (n = 43; 46.2%), with 33.3% rated "strong" (n = 31) and 20.4% "weak" (n = 19). Overall ratings reflected the methodological limitations typical of cross-sectional, correlational literature, namely limited control of confounding variables and selection bias.
Relationship Between Dissociation and Positive Symptoms
Global Positive Symptoms. A random-effect meta-analysis of 98 effects found a robust association between clinical and nonclinical positive psychotic symptoms and dissociation, r = .437 (95%CI: .386 −.486). Heterogeneity analyses indicated that there was considerable statistical inconsistency, Q(97) = 3135.421, P < .001, I 2 = 96.907; hence, caution should be taken when interpreting this summary effect. No influential cases were found, but the Egger's test indicated possible bias, t(96) = 5.222, P < .001. The imputation of 12 hypothetically missing studies using the trim-and-fill method led to a marginal decrease in the summary effect, which remained of moderate magnitude: r = .402 (95%CI: .353 −.448).
A subgroup analysis comparing clinical (k = 42) and nonclinical studies (k = 51) indicated that the relationship between dissociation and positive symptoms was significantly larger in nonclinical (r = .475, 95%CI: .426 −.521) than clinical studies (r = .388, 95%CI: .311 −.459; Q(1) = 3.902, P = .048). Considerable heterogeneity was apparent in both subgroup analyses (I 2 = 93.647% and 92.616%, respectively). There was no significant difference between correlational (r = .457, 95%CI: .420 −.492) and between-group effects (r = .337, 95%CI: .189 −.470) extracted from the primary studies (Q(1) = 2.821, P = .093).
We further examined associations between total positive symptoms and dissociation subtypes assessed by the DES-II. In this analysis, it was impossible to directly contrast the summary effect sizes pertaining to different subtypes due to nonindependence of the effects extracted from the primary studies. The analysis indicated that summary effects were generally similar in magnitude: absorption (k = 33; r = .460, 95%CI: .409 −.509), amnesia (k = 18, r = .357, 95%CI: .297 −.415), and depersonalization/derealization (k = 24, r = .405, 95%CI: .355 −.452).
A sensitivity analysis was conducted by restricting the above random-effect meta-analyses to studies that considered total measures of positive symptoms in clinical (eg, PANSS positive scale) and nonclinical samples (ie, total positive schizotypy measures like the SPQ). The results were largely comparable to those reported above. With 267 independent effects included for analysis, the summary effects for associations between positive symptoms and dissociation across clinical and nonclinical studies was r = .401 (95%CI: .305 −.489). There were high levels of heterogeneity, Q(26) = 384.884, P < .001, I 2 = 93.246, but no evidence of publication bias was found (t(26) = 1.808, P = .171). The summary effect for the association between dissociative experiences and positive symptoms was substantially larger in nonclinical (k = 9, r = .511, 95%CI: .430 −.583) than clinical studies (k = 17, r = .331, 95%CI: .208 −.444; Q(1) = 6.530, P = .011). Subgroup analyses focusing on dissociation subtypes found moderate-to-large associations for absorption (k = 6; r = .473, 95%CI: .381 −.556) but only small associations for amnesia (k = 2, r = .178, 95%CI: −.043 −.382) and depersonalization/derealization (k = 5, r = .181, 95%CI: .019 −.334). These two findings may be related, as absorption experiences typically fall on the "normal" (nonclinical) end of the dissociation continuum.
Hallucinations. A random-effect meta-analysis considering 50 effects found evidence of a robust but statistically heterogeneous association between hallucinatory experiences and dissociation: r = .461 (95%CI: .386 −.531), Q(49) = 2864.317, P < .001, I 2 = 98.289. No influential cases were identified, and inspection of the funnel plot and the Egger's test indicated no evidence of publication or other selection bias.
A subgroup analysis was carried out to contrast clinical (k = 18) with nonclinical studies (k = 30). After removing one potential outlier, the analysis indicated that the relationship between dissociation and hallucinatory experiences was equivalent across the two subgroups of studies: clinical, r = .432 (95%CI: .274 −.567) and nonclinical, r = .482 (95%CI: .416 −.543); Q(1) = 0.388, P = .534. A further subgroup analysis focusing on the DES-II dissociation subtypes indicated that summary affects were robust and significant in all cases: depersonalization/derealization (k = 20, r = .470, 95%CI: .416 −.521) followed by absorption (k = 23, r = .465, 95%CI: .394 −.531) and amnesia (k = 13, r = .388, 95%CI: .328 −.445).
An additional subgroup analysis was conducted to descriptively compare the effects obtained in studies considering hallucinations in different sensory modalities. These analyses could only be conducted for auditory (k = 15) and visual experiences (k = 4) due to a low number of studies that considered hallucinations in other domains. The findings indicated that the summary effects of auditory and visual hallucinations were r = .499 (95%CI: .413 −.575) and r = .476 (95%CI: .270 −.641), respectively.
Finally, a sensitivity analysis was conducted to clarify the results of these analyses by excluding effects extracted from 9 samples that used schizotypal measures of anomalous perception (which, although overlapping with hallucinatory experiences, considered a broader range of perceptual anomalies). After the exclusion of these studies, the random-effect meta-analysis of the remaining 41 effects found evidence of a robust but heterogeneous association between hallucinatory experiences and dissociation, with results comparable to those reported above; r = .453 (95%CI: .371 −.529), Q(40) = 1900.134, P < .001, I 2 = 97.895. The results of subgroup analyses contrasting clinical and nonclinical studies as well as studies focusing on the DES-II dissociation subtypes were likewise comparable to those reported in our main analyses.
Delusions. A random-effect meta-analysis with 30 effects found a moderate-to-large, but statistically heterogeneous, association between delusions and dissociation: r = .418 (95%CI: .370 −.464), Q(29) = 164.987, P < .001, I 2 = 82.423. There was no evidence of potentially influential cases or publication bias.
A subgroup analysis comparing nonclinical (k = 17) and clinical studies (k = 12) found a significantly larger summary effect in nonclinical samples: r = .480 (95%CI: .428 −.529) and r = .297 (95%CI: .238 −.354); Q(1) = 21.750, P < .001, respectively. Subgroup analyses focusing on DES-II subtypes indicated that that the summary effects of absorption (k = 8, r = .402; 95%CI: .315 −.482) were somewhat larger than those of depersonalization/derealization (k = 6, r = .305, 95%CI: .236 −.371) and amnesia (k = 4, r = .195, 95%CI: −.090 −.384).
Only a minority of studies assessed associations between specific delusional beliefs (eg, grandiose, somatic, bizarre) and dissociation. There was also considerable heterogeneity in the type of beliefs considered in these studies, which precluded our ability to carry out more fine-grained analyses.
Paranoia. After integrating 22 effects, the summary effect size for the relationship between dissociation and paranoia was r = .447 (95%CI: .393 −.499). Substantial statistical inconsistency was observed, Q(21) = 73.295, P < .001, I 2 = 71.349, but there was no evidence of publication bias or studies exerting undue influence on these findings.
A subgroup analysis carried out to compare clinical (k = 8) and nonclinical studies (k = 13) found that the association between dissociative experiences and paranoia was largely comparable across the two groups: r = .416 (95%CI: .260 −.551) and r = .470 (95%CI: .423 −.515) respectively; Q(1) = .507, P = .476. Further subgroup analyses indicated that the summary effects for the DES-II dissociative subtypes were broadly comparable: absorption (k = 6; r = .426, 95%CI: .280 −.552), amnesia (k = 5, r = .401, 95%CI: .256 −.529), and depersonalization/derealization (k = 6, r = .427, 95%CI: .307 −.533).
Relationship Between Dissociation and Negative Symptoms
Global Negative Symptoms. A meta-analysis considering 27 effects found a small and heterogeneous relationship between negative symptoms and dissociation: r = .138 (95%CI .065 −.209), Q(26) = 135.706, P < .001, I 2 = 80.841. Visual inspection of the funnel plot and Egger's test found no evidence of publication or other selection bias.
A subgroup analysis comparing clinical (k = 14) and nonclinical studies (k = 11) indicated that the relationship between dissociation and negative symptoms was significant in the nonclinical (r = .173, 95%CI: .101 −.242) but not the clinical samples (r = −.082, 95%CI: −.031 −.192). However, the differences in these summary effects were not significant: Q(1) = 1.827, P = .176. As only 1 study provided between-group effects, no subgroup analysis with correlational effects was conducted.
A sensitivity analysis was conducted on 13 studies that considered total measures of negative symptoms. These analyses indicated that the association between dissociative experiences and negative symptoms was not statistically significant: r = .0.084 (95%CI: −.025 −.191), Q(12) = 44.815, P = .129, I 2 = 73.233.
To explore potential associations between dissociation and more specific negative symptoms, we combined effects pertaining to the following categories:
Reduced Emotional Experience and/or Expressiveness. This analysis concerned a group of symptoms comprising anhedonia, flat/blunted/shallow/flattened affect, and emotional withdrawal. It included 11 effects and found a small and heterogeneous association between dissociative experiences and the symptoms under scrutiny: r = .128 (95%CI: .043 −.210), Q(10) = 36.529, P < .001, I 2 = 72.624.
Lack of Motivation, Asociality, and Withdrawal. This symptom category covered a lack of close relationships, poor rapport, desocialization, asociality, apathy, avolition, and lack of spontaneity. This random-effects meta-analysis considered 7 effects; a small but significant summary effect was observed: r = .190 (95%CI: .090 −.285), and heterogeneity was modest within these analyses: Q(6) = 12.394, P = .03, I 2 = 55.793.
Cognitive Symptoms. This cluster considered stereotyped thinking and difficulties in abstract thinking and attention. Only 3 effects were available for this analysis. A small summary effect was found: r = −.108 (95%CI: −.287 −.472) but heterogeneity statistics indicated substantial variation: Q(2) = 12.684, P < .001, I 2 = 87.248.
Relationship Between Dissociation and Disorganization
A random-effects meta-analysis including 12 effects led to a moderate summary effect pertaining to associations between disorganization symptoms and dissociation: r = .346 (95%CI: .249 −.436). Statistical heterogeneity was substantial, Q(11) = 74.051, P < .001, I2 = 85.145, but there was no evidence of publication bias or influential effects. However, one investigation had an uncharacteristically negative and significant effect size. A sensitivity analysis was conducted by removing this study. The results were broadly comparable to those of the main analysis above: r = .382 (95%CI: .296 −.461), Q(10) = 52.051, P < .001, I 2 = 81.099. As all studies provided data to compute correlational effects, no subgroup analysis of correlational and between-group effects was conducted.
A subgroup analysis comparing clinical (k = 5) and nonclinical (k = 6) studies indicated that the relationship between dissociation and disorganization was equivalent across the two samples: r = .348 (95%CI: .036 −.587) and r = .402 (95%CI: .337 −.463); Q-test(1) = .138, P = .710, respectively. There were no sufficient data to conduct subgroup analyses focusing on dissociation subtype, nor for total measures of disorganization.
Sensitivity Analyses for Study Quality
We conducted a final sensitivity analysis to evaluate the impact of including the 19 studies deemed methodologically weaker according to EPHHP ratings. Their exclusion had minimal impact on the overall findings of our meta-analyses focusing on positive symptoms, negative symptoms, and disorganization. In all cases, the summary effects and statistical heterogeneity statistics remained comparable to those reported in our main analyses.
Schizophr Bull. 2020;46(5):1104-1113. © 2020 Oxford University Press