title: Improving measurement properties of the Patient Health Questionnaire-9 with rating scale analysis.
abstract: OBJECTIVE
  The goal of this study was to explore the psychometric properties of the Patient Health Questionnaire-9 (PHQ-9; R. L. Spitzer, K. Kroenke, & J. B. W. Williams, 1999).
  
  
  METHODS
  Factor analysis and Rasch rating scale analysis were used to examine the psychometric properties of the PHQ-9. The sample consisted of 202 adults with spinal cord injury (SCI).
  
  
  RESULTS
  The PHQ-9 items appear to form a usefully unidimensional scale. One "double-barreled" item, "Moving or speaking so slowly that other people could have noticed or being so fidgety or restless that you've been moving around a lot more than usual," misfit the Rasch model. Category probability curves indicate respondent difficulty in distinguishing between the 2 intermediate rating scale categories: several days and more than half the days. Combining these categories eliminated this problem and resulted in all items fitting the measurement model.
  
  
  CONCLUSIONS
  The measurement properties of the PHQ-9 can be improved by collapsing rating scale categories and by restructuring several double- and triple-barreled items. Adopting these changes may improve sensitivity in measuring depression after SCI.
authors.affiliation: Center for Rehabilitation Outcomes Research, Rehabilitation Institute of Chicago. rwilliams@ric.org
authors.forename: Ryan T
authors.initials: RT
authors.lastname: Williams
authors.forename: Allen W
authors.initials: AW
authors.lastname: Heinemann
authors.forename: Rita K
authors.initials: RK
authors.lastname: Bode
authors.forename: Catherine S
authors.initials: CS
authors.lastname: Wilson
authors.forename: Jesse R
authors.initials: JR
authors.lastname: Fann
authors.forename: Denise G
authors.initials: DG
authors.lastname: Tate
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003866:Depressive Disorder / Q000175:diagnosis* / Q000523:psychology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011594:Psychometrics / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D013119:Spinal Cord Injuries / Q000523:psychology* / Q000534:rehabilitation*; D011795:Surveys and Questionnaires; D055815:Young Adult