title: A comparison of participants with non-participants in a population-based epidemiologic study: the Melbourne Visual Impairment Project.
abstract: OBJECTIVE
  Adequate participation in population-based studies in essential to ensure that the sample is representative of the population under investigation. Participants may differ from non-participants on important variables such as age, sex socioeconomic status, and general health factors. The Melbourne Visual Impairment Project (Melbourne VIP) is a population-based study designed to increase understanding of the prevalence and severity of common ocular disorders affecting people 40 years of age and over.
  
  
  OBJECTIVE
  The aim of this study was to determine the potential for any non-response bias by comparing data from participants and non-participants of the Melbourne VIP.
  
  
  METHODS
  Specific demographic and general variables were compared between the two groups. The variables included age, sex, education level, and social status. The reason for non-attendance was also recorded.
  
  
  RESULTS
  A total of 3271 (83%) eligible residents from the 9 sample areas were screened; 46% males and 54% females. Language spoken at home was significantly associated with participation. Residents whose main language at home was not English were less likely to attend the screening centre. (OR: 0.60; CI: 0.44-0.81). The main reasons given for non-attendance by eligible residents were lack of interest (6%), too busy to attend (4%), personal illness (2%), and attend own eye specialist (2%).
  
  
  CONCLUSIONS
  We believe these results will not impact significantly on the interpretation of gender and age-specific data from the Melbourne VIP.
authors.affiliation: Department of Ophthalmology, University of Melbourne, Victoria, Australia.
authors.forename: P M
authors.initials: PM
authors.lastname: Livingston
authors.forename: S E
authors.initials: SE
authors.lastname: Lee
authors.forename: C A
authors.initials: CA
authors.lastname: McCarty
authors.forename: H R
authors.initials: HR
authors.lastname: Taylor
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001315:Australia / Q000453:epidemiology; D015982:Bias; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D015994:Incidence; D008019:Life Style; D008297:Male; D008875:Middle Aged; D010358:Patient Participation / Q000706:statistics & numerical data; D015995:Prevalence; D012189:Retrospective Studies; D012923:Social Class; D014786:Vision Disorders / Q000175:diagnosis / Q000453:epidemiology*