Cognitive impairment in schizophrenia: clinical ratings are not a suitable alternative to neuropsychological testing.

Despite the fact that cognitive impairment rated with clinical rating scales has been shown to be a poor proxy for cognitive functioning measured with a performance-based assessment battery, studies are still using this approach to predict aspects of outcome in schizophrenia. In the current study 106 outpatients with chronic schizophrenia who had been stable both from a symptomatic and a medication perspective for a period of 6 months before study inclusion were investigated to assess the relationship between a clinical rating of cognitive impairment and the actual performance on neuropsychological tests. The cognitive component of the PANSS was compared to results from a neuropsychological test battery which was selected to cover domains known to be impaired in patients with schizophrenia. Correlations of the cognitive component of the PANSS with the individual neuropsychological tests were low. They ranged between 0.19 and 0.35. None of them was sufficiently high to indicate that the cognitive component of the PANSS adequately covers the cognitive dimension measured by the respective neuropsychological test. These data clearly show that clinical assessment of cognitive deficits by the PANSS is not a viable alternative to neuropsychological testing to obtain information about cognitive functioning in schizophrenia.