Effects of recruitment strategy on response rates and risk factor profile in two cardiovascular surveys

BACKGROUND: The study was set up to assess the effect of recruitment methods on participation rate, response bias and cardiovascular risk factor estimates. METHODS: Two random samples of men and women in Halifax County aged 25-74 were drawn from the same sampling frame. Their respective sizes were 1007 (NSHHS) and 3036 (MONICA) people. Recruitment by Nova Scotia Heart Health Survey (NSHHS) was through face-to-face contact, whereas the MONICA survey relied on invitation by mail. Outcome measures were response rates at various stages of the recruitment process and the differences in cardiovascular risk factor estimates. RESULTS: Face-to-face recruitment located 51% and mail recruitment located 47% of their respective samples; face-to-face recruitment resulted in fewer individuals who refused to participate in the survey, but also produced fewer who were prepared to provide blood samples in addition to answering questionnaires. By-mail recruits were more likely to have post-secondary education, but did not differ in the proportion of smokers, mean diastolic blood pressure or body mass index, if controlled for education level, gender and age. However, the mean systolic blood pressure was 5.7 mmHg higher and the mean cholesterol level 0.44 mmol/l lower in face-to-face recruits. CONCLUSIONS: Controlling for age, gender and education level eliminates the effect of recruitment bias on most cardiovascular risk factors estimates. The exceptions in our study were systolic blood pressure and cholesterol, where methodological factors may have played a role.