Can Clinicians Use the PHQ-9 to Assess Depression in People with Vision Loss?
Purpose: To investigate whether the Patient Health Questionnaire-9 (PHQ-9) possesses the essential psychometric characteristics to measure depressive symptoms in people with visual impairment.
Methods: The PHQ-9 scale was completed by 103 participants with low vision. These data were then assessed for fit to the Rasch model.
Results: The participants’ mean ± standard deviation (SD) age was 74.7 ± 12.2 years. Almost one half of them (n = 46; 44.7%) were considered to have severe vision impairment (presenting visual acuity <6/60 in the better eye). Disordered thresholds were evident initially. Collapsing the two middle categories produced ordered thresholds and fit to the Rasch model (χ2 = 10.1; degrees of freedom = 9; p = 0.34). The mean (SD) items and persons Fit Residual values were –0.31 (1.12) and –0.25 (0.78), respectively, where optimal fit of data to the Rasch model would have a mean = 0 and SD = 1. Unidimensionality was demonstrated confirming the construct validity of the PHQ-9 and there was no evidence of differential item functioning on a number of factors including visual disability. The person separation reliability value was 0.80 indicating that the PHQ-9 has satisfactory precision. There was a degree of mistargeting as expected in this largely non-clinically depressed sample.
Conclusions: Our findings demonstrate that the PHQ-9, when scaled with Rasch analysis, forms a linear interval measurement of depressive symptoms suitable for use in a vision impaired population.
Key Words: depression, low vision, PHQ-9, Rasch analysis.
Optometry & Vision Science 2009;86:139–145
Ecosse L. Lamoureux, PhD, H. Wen Tee, MBBS, Konrad Pesudovs, PhD, Julie F. Pallant, PhD, Jill E. Keeffe, PhD, and Gwen Rees, PhD
Singapore Eye Research Institute, Singapore National Eye Centre, Singapore (ELL), Centre for Eye Research Australia, University of Melbourne, Melbourne, Victoria, Australia (ELL, WHT, JEK, GR), NH&MRC Centre for Clinical Eye Research, Flinders University, Flinders Medical Centre-Australia, Bedford Park, South Australia, Australia (KP), School of Rural Health, Shepparton, University of Melbourne, Melbourne, Victoria, Australia (JFP), Vision CRC, Sydney, New South Wales, Australia (ELL, JEK), and The Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia (ELL, JEK, GR).
Accepted for publication 29 JUly 2008
© 2007 American Academy of Optometry
PHQ-9 for People with Vision Loss
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