title: Assessment of the psychometric properties of the Chinese Impact of Vision Impairment questionnaire in a population-based study: findings from the Singapore Chinese Eye Study.
abstract: OBJECTIVE
  We investigated whether the Chinese impact of vision impairment (IVI) questionnaire is valid to generate reliable person estimates in a population-based sample.
  
  
  METHODS
  VRQoL was measured using the 32-item Chinese version of the IVI questionnaire in the Singapore Chinese Eye Study (2009-2011), a population-based study of the prevalence and risk factors for VI and eye diseases in Chinese Singaporeans. Rasch analysis was used to assess the Chinese IVI's response category functioning, precision, unidimensionality, targeting and differential item functioning. The ability of the Chinese IVI to discriminate participants along the spectrum of VI demonstrated criterion validity.
  
  
  RESULTS
  Of the 3353 participants, 27.2 % (n = 912) had VI (presenting visual acuity <6/12, better eye). Response categories were collapsed from six to four to resolve disordered thresholds. The Chinese IVI initially demonstrated multidimensionality and was split into three scales: 'Reading and Accessing Information'; 'Mobility and Independence'; and 'Emotional Well-being'. All three scales were unidimensional and demonstrated excellent range-based precision (all reliability coefficients 0.97), following removal of three misfitting items. Mean person measures decreased with worsening VI (e.g. Reading: none (7.50 logits); mild (6.99 logits); moderate (6.44 logits); and severe (3.01 logits) VI; p < 0.001).
  
  
  CONCLUSIONS
  A three-dimensional 29-item Chinese IVI is a valid tool to assess the impact of VI on VRQoL in a large population-based sample, comprising over a quarter of participants with VI. The 28-item English IVI is also likely to be valid for use in population-based studies; however, this must be demonstrated empirically in future studies.
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Australia.
authors.forename: Eva K
authors.initials: EK
authors.lastname: Fenwick
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.
authors.forename: Peng Guan
authors.initials: PG
authors.lastname: Ong
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.|Duke-NUS Graduate Medical School, 8 College Road Level 4, Singapore, 169857, Singapore.
authors.forename: Charumathi
authors.initials: C
authors.lastname: Sabanayagam
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Australia.
authors.forename: Gwyn
authors.initials: G
authors.lastname: Rees
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Australia.
authors.forename: Jing
authors.initials: J
authors.lastname: Xie
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Australia.
authors.forename: Edith
authors.initials: E
authors.lastname: Holloway
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.|Department of Ophthalmology, National University of Singapore and National University Health System, Singapore, Singapore.|Duke-NUS Graduate Medical School, 8 College Road Level 4, Singapore, 169857, Singapore.
authors.forename: Ching-Yu
authors.initials: CY
authors.lastname: Cheng
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.|Department of Ophthalmology, National University of Singapore and National University Health System, Singapore, Singapore.|Duke-NUS Graduate Medical School, 8 College Road Level 4, Singapore, 169857, Singapore.
authors.forename: Tien Y
authors.initials: TY
authors.lastname: Wong
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.
authors.forename: Blanche
authors.initials: B
authors.lastname: Lim
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore.
authors.forename: Pok Chien
authors.initials: PC
authors.lastname: Tan
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, University of Melbourne, Melbourne, Australia. ecosse.lamoureux@duke-nus.edu.sg.|Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore. ecosse.lamoureux@duke-nus.edu.sg.|Department of Ophthalmology, National University of Singapore and National University Health System, Singapore, Singapore. ecosse.lamoureux@duke-nus.edu.sg.|Duke-NUS Graduate Medical School, 8 College Road Level 4, Singapore, 169857, Singapore. ecosse.lamoureux@duke-nus.edu.sg.
authors.forename: Ecosse L
authors.initials: EL
authors.lastname: Lamoureux
mesh_terms: D000328:Adult; D000368:Aged; D044466:Asian People; D005260:Female; D006801:Humans; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D011159:Population Surveillance; D015995:Prevalence; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology; D015203:Reproducibility of Results; D012307:Risk Factors; D018434:Sickness Impact Profile; D012846:Singapore; D011795:Surveys and Questionnaires / Q000592:standards; D014786:Vision Disorders / Q000523:psychology*
keywords: Chinese impact of vision impairment questionnaire; Population-based; Rasch analysis; Reliability; Vision impairment