title: Reliability of standard health assessment instruments in a large, population-based cohort study.
abstract: OBJECTIVE
  The Millennium Cohort Study began in 2001 using mail and Internet questionnaires to gather occupational and environmental exposure, behavioral risk factor, and health outcome data from a large, population-based US military cohort. Standardized instruments, including the Patient Health Questionnaire, the Medical Outcomes Study Short Form-36 for Veterans, and the Posttraumatic Stress Disorder (PTSD) Checklist-Civilian Version, have been validated in various populations. The purpose of this study was to investigate internal consistency of standardized instruments and concordance of responses in a test-retest setting.
  
  
  METHODS
  Cronbach alpha coefficients were used to investigate the internal consistency of standardized instruments among 76,742 participants. Kappa statistics were calculated to measure stability of aggregated responses in a subgroup of 470 participants who voluntarily submitted an additional survey within 6 months of their original submission.
  
  
  RESULTS
  High internal consistency was found for 14 of 16 health components, with lower internal consistency found among two alcohol components. Substantial test-retest stability was observed for stationary variables, while moderate stability was found for more dynamic variables that measured conditions with low prevalence.
  
  
  CONCLUSIONS
  These results substantiate internal consistency and stability of several standard health instruments applied to this large cohort. Such reliability analyses are vital to the integrity of long-term outcome studies.
authors: Department of Defense Center for Deployment Health Research at the Naval Health Research Center, San Diego, CA 92186-5122, USA. Smith@nhrc.navy.mil
authors: Tyler C
authors: TC
authors: Smith
authors: Besa
authors: B
authors: Smith
authors: Isabel G
authors: IG
authors: Jacobson
authors: Thomas E
authors: TE
authors: Corbeil
authors: Margaret A K
authors: MA
authors: Ryan
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D008889:Military Personnel; D011594:Psychometrics; D015203:Reproducibility of Results; D012107:Research Design; D013313:Stress Disorders, Post-Traumatic / Q000453:epidemiology*; D011795:Surveys and Questionnaires / Q000592:standards*; D014481:United States / Q000453:epidemiology; D014728:Veterans