title: Rasch validation of the PHQ-9 in people with visual impairment in South India.
abstract: BACKGROUND
  The Patient-Health Questionnaire (PHQ-9) is a widely used screening instrument for depression. Recently, its properties as a measure were investigated using Rasch analysis in an Australian population with visual impairment (VI) and it was demonstrated to possess excellent measurement properties, but the response scale required shortening (modified PHQ-9). However, further validation was recommended to substantiate its use with the growing population of VI. Therefore, we aimed to use Rasch analysis to evaluate the measurement properties of the modified PHQ-9 in an Indian population with VI.
  
  
  METHODS
  303 patients with VI (mean age 40.2 years; 71% male) referred to Vision Rehabilitation Centres were administered the PHQ-9 by trained interviewer. Rasch analysis was used to investigate the psychometric properties of the modified PHQ-9.
  
  
  RESULTS
  Rasch analysis showed good fit to the model, no misfitting items and an acceptable person separation reliability (0.82). Dimensionality testing supported combining 9 items to create a total score. Targeting was sub-optimal (-1.30 logits); more difficult items are needed. One item ('trouble falling asleep') showed notable differential item functioning, DIF (1.18 logits) by duration of VI.
  
  
  CONCLUSIONS
  The generalisability of these results might be restricted to patients with VI presenting to a tertiary eye care centre.
  
  
  CONCLUSIONS
  Except for DIF, the performance of the modified PHQ-9 is consistent with that of the original, albeit in a different cultural context (Indian population with VI). Clinicians/researchers can readily use the modified PHQ-9 without formal training in Rasch procedures given the provision of ready-to-use spreadsheets that convert raw to Rasch-scaled scores. However the conversions will apply only if the sample being tested is similar to that of the present study.
authors: Meera and L.B. Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L.V. Prasad Eye Institute, Kallam Anji Reddy Campus, L.V. Prasad Marg, Banjara Hills, Hyderabad 500034, Andhra Pradesh, India. Electronic address: vijayagothwal@gmail.com.
authors: Vijaya K
authors: VK
authors: Gothwal
authors: Meera and L.B. Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L.V. Prasad Eye Institute, Kallam Anji Reddy Campus, L.V. Prasad Marg, Banjara Hills, Hyderabad 500034, Andhra Pradesh, India.
authors: Deepak K
authors: DK
authors: Bagga
authors: Meera and L.B. Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L.V. Prasad Eye Institute, Kallam Anji Reddy Campus, L.V. Prasad Marg, Banjara Hills, Hyderabad 500034, Andhra Pradesh, India.
authors: Rebecca
authors: R
authors: Sumalini
mesh_terms: D000328:Adult; D003863:Depression / Q000175:diagnosis*; D003866:Depressive Disorder / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007194:India; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D014786:Vision Disorders / Q000523:psychology*; D055815:Young Adult
keywords: Depression; Patient Health Questionnaire-9; Rasch analysis; Visual impairment