Social functioning and formal thought disorder in schizophrenia: A Bayesian meta-analysis.

BACKGROUND: Formal thought disorder (FTD) is a key determinant of social functioning in schizophrenia. However, existing syntheses have not differentiated positive versus negative FTD dimensions, which have distinct trajectories, mechanisms, and treatment implications. We examined the differential associations of positive and negative FTD with social functioning. METHODS: A comprehensive systematic review with stricter inclusion criteria to update prior meta-analyses, searching Scopus and PubMed for publications up to 31 January 2026. Bayesian random-effects meta-analyses were performed separately for negative FTD (k = 7 studies, N = 1226) and positive FTD (k = 24, N = 4072). Bias was assessed using a modified Newcastle-Ottawa Scale. Robust Bayesian methods assessed publication bias. Protocol pre-registered with OSF: 10.17605/OSF.IO/WMT3X. RESULTS: Both dimensions showed negative associations with social functioning. Positive FTD demonstrated a robust pooled effect (r = -0.31, 95% CrI: -0.40 to -0.20) with extreme evidence (BF10 > 100, posterior probability ~100%). Negative FTD showed a smaller effect (r = -0.21, 95% CrI: -0.38 to 0.000) with moderate evidence (BF10 = 7.97, posterior probability = 88.9%). Positive FTD accounts for more variance in functioning than negative FTD, but this difference is not robust due to paucity of negative FTD studies. High heterogeneity (I2 > 76%), unexplained by known moderators, indicates substantial variation across study settings. CONCLUSIONS: Both FTD dimensions link to poorer social functioning, with stronger evidence for positive FTD due to more studies and larger samples. Positive FTD may affect social functioning by disrupting communicative competence, highlighting a need for interventions targeting communication deficits.