title: The patient health questionnaire-9: validation among patients with glaucoma.
abstract: BACKGROUND
  Depression and anxiety are two common normal responses to a chronic disease such as glaucoma. This study analysed the measurement properties of the depression screening instrument - Patient Health Questionnaire-9 (PHQ-9) using Rasch analysis to determine if it can be used as a measure.
  
  
  METHODS
  In this hospital-based cross-sectional study, the PHQ-9 was administered to primary glaucoma adults attending a glaucoma clinic of a tertiary eye care centre, South India. All patients underwent a comprehensive clinical evaluation. Patient demographics and sub-type of glaucoma were abstracted from the medical record. Rasch analysis was used to investigate the following properties of the PHQ-9: behaviour of the response categories, measurement precision (assessed using person separation reliability, PSR; minimum recommended value 0.80), unidimensionality (assessed using item fit [0.7-1.3] and principal components analysis of residuals), and targeting.
  
  
  RESULTS
  198 patients (mean age ± standard deviation  = 59.83±12.34 years; 67% male) were included. The native PHQ-9 did not fit the Rasch model. The response categories showed disordered thresholds which became ordered after category reorganization. Measurement precision was below acceptable limits (0.62) and targeting was sub-optimal (-1.27 logits). Four items misfit that were deleted iteratively following which a set of five items fit the Rasch model. However measurement precision failed to improve and targeting worsened further (-1.62 logits).
  
  
  CONCLUSIONS
  The PHQ-9, in its present form, provides suboptimal assessment of depression in patients with glaucoma in India. Therefore, there is a need to develop a new depression instrument for our glaucoma population. A superior strategy would be to use the item bank for depression but this will also need to be validated in glaucoma patients before deciding its utility.
authors.affiliation: Meera and L B Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L V Prasad Eye Institute, Hyderabad, India.
authors.forename: Vijaya K
authors.initials: VK
authors.lastname: Gothwal
authors.affiliation: Meera and L B Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L V Prasad Eye Institute, Hyderabad, India.
authors.forename: Deepak K
authors.initials: DK
authors.lastname: Bagga
authors.affiliation: Meera and L B Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L V Prasad Eye Institute, Hyderabad, India.
authors.forename: Seelam
authors.initials: S
authors.lastname: Bharani
authors.affiliation: Meera and L B Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L V Prasad Eye Institute, Hyderabad, India.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Sumalini
authors.affiliation: Bausch and Lomb School of Optometry, L V Prasad Eye Institute, Hyderabad, India.
authors.forename: Shailaja P
authors.initials: SP
authors.lastname: Reddy
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001007:Anxiety / Q000175:diagnosis; D003430:Cross-Sectional Studies; D003863:Depression / Q000175:diagnosis; D005260:Female; D005901:Glaucoma / Q000523:psychology*; D006306:Health Surveys / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D011795:Surveys and Questionnaires; D062606:Tertiary Care Centers; D055815:Young Adult