We aimed to identify best predictors of cognitive and functional disability in chronic schizophrenia over time.

We examined 95 hospitalised patients with schizophrenia (DSM-IV criteria) in a long stage unit and 53 healthy controls (matched for age, gender, and years of education). Neuropsychological assessment included tests for Verbal Memory, Working Memory, Executive Functioning and Processing Speed. Functional Disability was assessed with the Disability Assessment Schedule (DAS-WHO) both at baseline and 6 months after.

As expected, patients" performance was significantly lower than healthy comparison subjects on all neurocognitive variables at baseline. Most, but not all, neurocognitive measures were positively correlated with the Functional Disability domains at follow up, including Self Care Management, Vocational Outcome, Family Contact and Social Competence. Results of mediation analyses suggest that all significant relationships identified between cognitive measures and functional outcome were significantly mediated by the Index Processing Speed (PS) with various effects ((between p < 0.05 for PS (z = -2.06) and p < 0.01 for PS (z = -3.01)).

Our data show that Processing Speed plays a determinant role in the relationship among neurocognitive symptoms and Self Care, Vocational Outcome and Social Competence. the model emphasizes the role of PS as the best longitudinal predictor of the level of autonomy in chronic patients with schizophrenia. PS acts as a pathway through which VM, EF and WM predict the course of patients’ functional ability over time.