Reduction of selection bias in primary prevention of cardiovascular disease through involvement of primary health care

OBJECTIVE: To examine selection bias in social and health factors in a community intervention programme for the prevention of cardiovascular disease by comparing programme data with both census data and a random sample of the same population. DESIGN: Cross sectional studies. SETTING: All 35 primary health care centres in Västerbotten County, Sweden. SUBJECTS: 24,870 individuals who during 1992 and 1993 became 30, 40, 50 or 60 years of age. MAIN OUTCOME MEASURES: Total income, socio-economic group, employment, education, body mass index (BMI), total cholesterol, systolic and diastolic blood pressure, and daily smoking. RESULTS: The differences in social characteristics between participants and non-participants were marginal, indicating that the social selection bias was small. However, unemployment, low income, and younger age tended to be associated with somewhat lower preference to participate. The overall pattern of health status, as measured by risk factors, was similar rather than dissimilar. While the participants in the intervention health survey had lower mean total cholesterol, their blood pressure was generally higher compared with the reference random sample. CONCLUSIONS: The primary health care system in Sweden might serve as a useful base for educational health counselling, at least within a community intervention programme, for all levels of society.