A psychometric analysis of 2 interview-based measures of cognitive deficits was conducted: the 21-item Clinical Global Impression of Cognition in Schizophrenia (CGI-CogS; Ventura et al., 2008), and the 20-item Schizophrenia Cognition Rating Scale (SCoRS; Keefe et al., 2006), which were administered on 2 occasions to a sample of people with schizophrenia. Traditional psychometrics, bifactor analysis, and item response theory methods were used to explore item functioning and dimensionality and to compare instruments.

Reise SP, Ventura J, Keefe RSE, Baade LE, Gold JM, Green MF, Kern RS, Mesholam-Gately R, Nuechterlein KH, Seidman LJ, Bilder RM. Bifactor and item response theory analyses of interviewer report scales of cognitive impairment in schizophrenia.  Psychological Assessment, 2011; 23(1): 245-261.  (PMCID: PMC3183749).