Theory of mind in schizophrenia: meta-analysis.

Background: Mentalising impairment (an impaired ability to think about people in terms of their mental states) has frequently been associated with schizophrenia.

Aims: To assess the magnitude of the deficit and analyse associated factors.

Method: Twenty-nine studies of mentalising in schizophrenia (combined n=1518), published between January 1993 and May 2006, were included to estimate overall effect size. Study descriptors predicted to influence effect size were analysed using weighted regression-analysis techniques. Separate analyses were performed for symptom subgroups and task types.

Results: The estimated overall effect size was large and statistically significant (d=-1.255, P<0.0001) and was not significantly affected by sample characteristics. All symptom subgroups showed significant mentalising impairment, but participants with symptoms of disorganisation were significantly more impaired than the other subgroups (P<0.01).

Conclusions: This meta-analysis showed significant and stable mentalising impairment in schizophrenia. The finding that patients in remission are also impaired favours the notion that mentalising impairment represents a possible trait marker of schizophrenia.