title: Factor structure of cognition and functional capacity in two studies of schizophrenia and bipolar disorder: Implications for genomic studies.
abstract: OBJECTIVE
  Impairments in cognition and everyday functioning are common in schizophrenia and bipolar disorder (BPD). In this article, we present factor analyses of cognitive and functional capacity (FC) measures based on 2 studies of schizophrenia (SCZ) and bipolar I disorder (BPI) using similar methods. The overall goal of these analyses was to determine whether performance-based assessments should be examined individually, or aggregated on the basis of the correlational structure of the tests, as well as to evaluate the similarity of factor structures of SCZ and BPI.
  
  
  METHODS
  Veterans Affairs Cooperative Studies Program Study #572 (Harvey et al., 2014) evaluated cognitive and FC measures among 5,414 BPI and 3,942 SCZ patients. A 2nd study evaluated similar neuropsychological (NP) and FC measures among 368 BPI and 436 SCZ patients. Principal components analysis, as well as exploratory and CFAs, were used to examine the data.
  
  
  RESULTS
  Analyses in both datasets suggested that NP and FC measures were explained by a single underlying factor in BPI and SCZ patients, both when analyzed separately or as in a combined sample. The factor structure in both studies was similar, with or without inclusion of FC measures; homogeneous loadings were observed for that single factor across cognitive and FC domains across the samples.
  
  
  CONCLUSIONS
  The empirically derived factor model suggests that NP performance and FC are best explained as a single latent trait applicable to people with SCZ and BPD. This single measure may enhance the robustness of the analyses relating genomic data to performance-based phenotypes.
authors.affiliation: Department of Research Service, Bruce W. Carter Miami Veterans Affairs Medical Center.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Harvey
authors.affiliation: Clinical Epidemiology Research Center, Veterans Affairs Connecticut Healthcare System.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Aslan
authors.affiliation: Department of Statistics, Yale Graduate School of Arts and Sciences, Yale University.
authors.forename: Mengtian
authors.initials: M
authors.lastname: Du
authors.affiliation: Clinical Epidemiology Research Center, Veterans Affairs Connecticut Healthcare System.
authors.forename: Hongyu
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Department of Psychiatry Service, James J. Peters Veterans Affairs Medical Center.
authors.forename: Larry J
authors.initials: LJ
authors.lastname: Siever
authors.affiliation: Department of Epidemiology, Bloomberg School of Public Health.
authors.forename: Ann
authors.initials: A
authors.lastname: Pulver
authors.affiliation: Massachusetts Veteran Epidemiology Research and Information Center, Veterans Affairs Boston Healthcare System.
authors.forename: J Michael
authors.initials: JM
authors.lastname: Gaziano
authors.affiliation: Clinical Epidemiology Research Center, Veterans Affairs Connecticut Healthcare System.
authors.forename: John
authors.initials: J
authors.lastname: Concato
mesh_terms: D000203:Activities of Daily Living; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001714:Bipolar Disorder / Q000235:genetics* / Q000523:psychology*; D003071:Cognition; D003072:Cognition Disorders / Q000235:genetics*; D005163:Factor Analysis, Statistical; D005260:Female; D023281:Genomics; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D010641:Phenotype; D012559:Schizophrenia / Q000235:genetics*; D012565:Schizophrenic Psychology; D014481:United States; D014728:Veterans / Q000523:psychology / Q000706:statistics & numerical data