Total and cause specific mortality among participants and non-participants of population based health surveys:: a comprehensive follow up of 54,372 Finnish men and women

Study objective: To assess total and cause specific mortality among participants and non-participants of large population based health surveys. Design: A prospective follow up study. Baseline surveys were conducted in 1972, 1977, 1982, 1987, and 1992. Study end points were overall, cardiovascular, cancer and violent mortality, and deaths related to smoking and alcohol. Study cohorts were followed up until the end of 2000 through computerised record linkage. All analyses were adjusted for age. Setting: Finland. Participants: Participants and non-participants of five population based risk factor surveys. The samples included 54 372 men and women aged 25 to 64 years at baseline. Main results: The average participation rate was 81.7% among men and 87% among women. At eight year follow up, the non-participating men had twice and non-participating women 2.5- fold higher overall mortality than the participating men and women. Non-participants had also significantly higher cause specific mortality, except cancer and smoking related mortality among women. Relative differences in mortality were largest in violent and alcohol related deaths. Non-participants had considerably higher overall mortality than smoking participants, and their mortality was threefold compared with non-smoking participants. Conclusions: Observed differences in mortality show that health behaviour and health status substantially differ between non-participants and participants. Low participation rate may considerably bias the results of population based health surveys.