title: Can clinicians use the PHQ-9 to assess depression in people with vision loss?
abstract: OBJECTIVE
  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 (chi = 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.
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore. ecosse@unimelb.edu.au
authors.forename: Ecosse L
authors.initials: EL
authors.lastname: Lamoureux
authors.forename: H Wen
authors.initials: HW
authors.lastname: Tee
authors.forename: Konrad
authors.initials: K
authors.lastname: Pesudovs
authors.forename: Julie F
authors.initials: JF
authors.lastname: Pallant
authors.forename: Jill E
authors.initials: JE
authors.lastname: Keeffe
authors.forename: Gwen
authors.initials: G
authors.lastname: Rees
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D001766:Blindness / Q000150:complications* / Q000523:psychology; D003863:Depression / Q000175:diagnosis* / Q000209:etiology; D005260:Female; D006801:Humans; D008297:Male; D011594:Psychometrics / Q000379:methods; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D014792:Visual Acuity