Supplementary Material for: Negative Symptoms and Executive Function in Schizophrenia: Does Their Relationship Change with Illness Duration?

Background: Negative symptoms and cognitive dysfunction are of crucial functional and prognostic importance in schizophrenia. However, the nature of the relationship between them and the factors that may influence it have not been well established. Aims: To investigate whether the relationship between negative symptoms and executive function changes according to the duration of illness in schizophrenia. Methods: The Positive and Negative Syndrome Scale was used to assess psychopathology and the Wisconsin Card Sorting Test (WCST) to evaluate executive function in a sample of 200 schizophrenic patients who were classified in 3 groups according to their duration of illness: up to 5 years (short duration group), 6-20 years (intermediate duration group) and over 20 years of illness (long duration group). Results: Medium-sized correlations were found between negative symptoms and WCST performance as assessed by the number of completed categories in all 3 groups. However, differences were found according to the duration of schizophrenia. For patients in the short duration group, negative symptoms correlated with WCST nonperseverative errors, but for those in the long duration group the correlation was with perseverative errors. Conclusion: We found a differential relationship between negative and cognitive symptoms in different stages of schizophrenia. Illness duration should be considered when studying the relationship between negative symptoms and cognition.