title: Investigating the effect of nonparticipation using a population-based case-control study on myocardial infarction.
abstract: OBJECTIVE
  To characterize non-participants in a population-based study on cardiovascular diseases and investigate the effect of non-participation on risk estimates for myocardial infarction.
  
  
  METHODS
  Using random digit dialing we obtained full information for 1054 adults (60.8% female), while 345 eligible individuals (72.5% female) declined the invitation to participate, but answered a limited set of questions by telephone. Risk of myocardial infarction was estimated using 474 cases (19.4% females) admitted with a first acute myocardial infarction.
  
  
  RESULTS
  Participation proportion was 99.0% for cases and 70.0% for population controls. Population non-participants were older (61.6 vs. 58.5 years, for males, and 62.9 vs. 57.7 years for females) and more frequently women (66.3% vs. 74.7%, p < 0.001); males tended to be non-drinkers and to have had a blood test during the previous year; females were additionally more often non-smokers. Crude and adjusted risk estimates for myocardial infarction were generally similar regardless of considering the information provided by non-participants.
  
  
  CONCLUSIONS
  In this South European population, demographic and social characteristics associated with the decision to participate in a community investigation were different from those usually described in Northern European or American populations. However, their characteristics did not influence the direction or the magnitude of myocardial infarction risk estimates.
authors.affiliation: Department of Hygiene and Epidemiology, University of Porto Medical School, Porto, Portugal.
authors.forename: Elisabete
authors.initials: E
authors.lastname: Ramos
authors.forename: Carla
authors.initials: C
authors.lastname: Lopes
authors.forename: Henrique
authors.initials: H
authors.lastname: Barros
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D015982:Bias; D016022:Case-Control Studies; D005191:Family Characteristics; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000453:epidemiology*; D011174:Portugal / Q000453:epidemiology; D045808:Refusal to Participate; D018570:Risk Assessment; D012737:Sex Factors