Investigating the effect of nonparticipation using a population-based case–control study on myocardial infarction

Purpose 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.