Research Article

Factor Structure of Neurocognition and Functional Capacity in Schizophrenia: A Multidimensional Examination of Temporal Stability

Philip D. Harvey^a1a2 c1, Tenko Raykov^a3, Elizabeth W. Twamley^a4a5, Lea Vella^a6, Robert K. Heaton^a4 and Thomas L. Patterson^a4

^a1 Department of Psychiatry, University of Miami Miller School of Medicine, Miami, Florida

^a2 Research Service, Miami VA Medical Center, Miami, Florida

^a3 Department of Education and Measurement, Michigan State University, East Lansing, Michigan

^a4 Department of Psychiatry, UCSD Medical Center, La Jolla, California

^a5 Psychiatry Service, San Diego VA Medical Center, La Jolla, California

^a6 Department of Psychology, UCSD-SDSU Joint Doctoral Program, San Diego, California

Abstract

Although neurocognition is commonly described in terms of different functional domains, some factor analytic studies have suggested a simpler dimensional structure for neuropsychological (NP) tests in patients with schizophrenia. Standardized tasks of everyday functioning, or tests of “functional capacity” (FC), are viewed differently from traditional NP tests, and are hence used as a co-primary measure in treatment studies. However, FC and NP tests have been found to be highly correlated. In fact, a recent study of ours suggested that performances on these different types of tasks constituted a single latent trait in a cross-sectional analysis. The current study examined the longitudinal factor structure of a combined set of NP and FC tests. Patients with schizophrenia (n = 195) were examined at two assessment occasions separated by periods ranging from 6 weeks to 6 months. Participants were assessed with the MATRICS Consensus Cognitive Battery (MCCB) and two performance-based assessments of FC. A single latent trait was extracted using full information maximum likelihood procedures, and its temporal stability was examined in terms of: stability of the latent trait scores, the inter-correlations of the three indicators of the latent trait, and the stability of loadings for the FC and NP items underlying the latent trait at the two measurement occasions. All indices of temporal stability were confirmed, with stability not related to follow-up duration. Variation in clinical symptoms and treatments across the measurement occasions was negligible. These findings raise the question of whether cognitive abilities measured by NP tests and FC instruments are tapping a single ability construct, which might have shared causal influences as well. (JINS, 2013, 19, 1–8)

(Received September 10 2012)

(Revised January 18 2013)

(Accepted January 22 2013)

Keywords

• Neuropsychology;
• Disability;
• Latent traits;
• Longitudinal studies;
• Functional capacity;
• Linear models

Correspondence:

^c1 Correspondence and reprint requests to: Philip D. Harvey, Department of Psychiatry and Behavioral Sciences, University of Miami Miller School of Medicine, 1120 NW 14^th Street, Suite 1450, Miami, FL 33136. E-mail: philipdharvey1@cs.com