title: Impact of resurvey non-response on the associations between baseline risk factors and cardiovascular disease mortality: prospective cohort study.
abstract: BACKGROUND
  Selection bias in observational epidemiology--the notion that people who participate in a study are fundamentally different from those who do not--is a perennial concern. In cohort studies, a potentially important but little investigated manifestation of selection bias is the distortion of the exposure-disease relationship according to participation status.
  
  
  METHODS
  Seven years after the original UK Health and Lifestyle Survey (HALS1; N = 6484), attempts were made to resurvey participants (HALS2). The baseline characteristics, mortality experience following the completion of HALS2 and, finally, the baseline risk factor-cardiovascular disease (CVD) mortality gradients in HALS2 non-participants (N = 1894) and participants (N = 4590) were compared.
  
  
  RESULTS
  Resurvey non-participants, based on data from HALS1, were younger, were of lower social class and had a lower prevalence of hypertension or self-reported limiting long-standing illness, but a higher prevalence of psychological distress (p < or = 0.027). The risk of death from future CVD was significantly higher in those baseline study members who did not participate in HALS2. However, the magnitude of the association between a series of risk factors and CVD mortality was essentially the same in the HALS2 non-participants and participants (p value for interaction > or = 0.108).
  
  
  CONCLUSIONS
  In the present cohort study, non-response at resurvey did not bias the observed associations between baseline risk factors and later CVD mortality. Future studies should also examine the impact of non-response to baseline surveys on these relationships.
authors: Medical Research Council Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK. david-b@sphsu.mrc.ac.uk
authors: G D
authors: GD
authors: Batty
authors: C R
authors: CR
authors: Gale
mesh_terms: D000328:Adult; D015982:Bias; D002318:Cardiovascular Diseases / Q000209:etiology / Q000401:mortality*; D006306:Health Surveys; D006801:Humans; D008019:Life Style; D059012:Lost to Follow-Up; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D018570:Risk Assessment; D015983:Selection Bias; D006113:United Kingdom / Q000453:epidemiology