The patient health questionnaire-9: validation among patients with glaucoma

PLoS One. 2014 Jul 7;9(7):e101295. doi: 10.1371/journal.pone.0101295. eCollection 2014.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Anxiety / diagnosis
  • Cross-Sectional Studies
  • Depression / diagnosis
  • Female
  • Glaucoma / psychology*
  • Health Surveys / methods*
  • Humans
  • Male
  • Middle Aged
  • Psychometrics
  • Surveys and Questionnaires*
  • Tertiary Care Centers
  • Young Adult

Grants and funding

This study was supported by the Hyderabad Eye Research Foundation, Hyderabad, India. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.