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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.


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.


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.


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.

Autor: Vijaya K. Gothwal , Deepak K. Bagga, Seelam Bharani, Rebecca Sumalini, Shailaja P. Reddy



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