Clinical global impression of cognition in schizophrenia (CGI-CogS): Reliability and validity of a co-primary measure of cognition

BackgroundCognitive deficits are core features of schizophrenia that have been associated reliably with functional outcomes and now are a focus of treatment research. New rating scales are needed to complement current psychometric testing procedures, both to enable wider clinical use, and to serve as endpoints in clinical trials.MethodsSubjects were 35 schizophrenia patient-and-caregiver pairs recruited from the UCLA and West Los Angeles VA Outpatient Psychiatry Departments. Participants were assessed with the Clinical Global Impression of Cognition in Schizophrenia (CGI-CogS), an interview-based rating scale of cognitive functioning, on 3 occasions (baseline, 1 month, and 3 months). A computerized neurocognitive battery (Cogtest), an assessment of functioning, and symptom measures were administered at two occasions (baseline and one month).ResultsThe CGI-CogS ratings generally showed a high level of internal consistency (Cronbach's alpha = .69 to .96), adequate levels of inter-rater reliability (ICC's = .71 to .80), and high test–retest stability (ICC's = .92 to .95). Correlations of caregiver and rater global (but not “patient only rating”) CGI-CogS ratings with neurocognitive performance were in the moderate range (r's = − .27 to − .48), while most of the correlations with functional outcome were moderate to high (r's = − .41 to − .72). In fact, the CGI-CogS ratings were significantly more correlated with Social Functioning than were objective neurocognitive test scores (p = .02) and showed a trend in the same direction for predicting Instrumental Functioning (p = .06). We found moderate correlations between CGI-CogS global ratings and PANSS positive (r's = .36 to .49) and SANS negative symptoms (r = .41 to .61), but not with BPRS depression (r's = .11 to .13).ConclusionsAn interview-based measure of cognition demonstrated high internal consistency, good inter-rater reliability, and high test–retest reliability. Caregiver ratings appear to add important clinical information over patient-only ratings. The CGI-CogS showed moderate validity with respect to neurocognitive performance and functional outcome, and correlations of CGI-CogS with functional outcomes were stronger than correlations of objective neurocognitive performance with functional outcomes. The CGI-CogS appears to offer a reliable and valid method for clinical rating of cognitive deficits and their impact on everyday functioning in schizophrenia.