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Drop-out and newcomer bias in a community cardiovascular follow-up study
P L Jooste1, D Yach, H J Steenkamp
1Research Institute for Nutritional Diseases, South African Medical Research Council, Tygerberg.
Insights
Community follow-up studies face bias from drop-out and newcomer participants. Drop-outs had lower education and higher smoking rates, impacting coronary risk factor analysis.
Area of Science:
- Epidemiology
- Public Health
- Cardiovascular Disease Research
Background:
- Longitudinal community studies are crucial for understanding disease progression and risk factors.
- Participant attrition (drop-out) and new participant enrollment (newcomers) can introduce significant bias in follow-up studies.
- Assessing these biases is vital for the accurate interpretation of study findings.
Purpose of the Study:
- To investigate drop-out bias and newcomer bias in a community-based coronary risk factor follow-up study.
- To identify characteristics of participants who dropped out and those who entered the study late.
- To evaluate the impact of these biases on coronary risk factor assessment.
Main Methods:
- A three-community coronary risk factor study with a baseline cross-sectional survey (7188 participants, aged 15-64).
- A four-year intervention period followed by a follow-up cross-sectional study (6283 participants, aged 19-68).
- Analysis of non-response rates, demographic, and risk factor differences between stayers, drop-outs, and newcomers.
Main Results:
- Overall non-response rates were 45% for men and 42% for women, with higher rates in younger age groups (15-24 years).
- Drop-outs at baseline were more likely to have lower educational qualifications and be smokers compared to stayers.
- Newcomers at follow-up showed similar coronary risk factors to stayers, with only slightly higher, non-significant, smoking rates.
Conclusions:
- Drop-out bias significantly affects community follow-up studies, particularly concerning educational attainment and smoking habits.
- Newcomer bias appears less pronounced in this study, but warrants consideration.
- Researchers must assess and account for both drop-out and newcomer biases before finalizing data evaluations in longitudinal community studies.
Abstract:
Bias resulting from a loss of baseline subjects at follow-up (drop-out), and newcomer bias resulting from subjects entering the study at the follow-up stage, were investigated in a three-community coronary risk factor follow-up study. The study consisted of a cross-sectional baseline study on 7188 participants aged 15 to 64 years, a four-year intervention period and a follow-up cross-sectional study in the same communities on 6283 participants aged 19 to 68 years. The overall non-response rate of 45% in men and 42% in women varied from 30 to 79% in the various age and sex groups, with the biggest drop-out rate occurring in the youngest age group of 15 to 24 years. At baseline drop-outs were more likely to have lower educational qualifications than those who participated in both the baseline and follow-up studies (stayers) and included significantly more smokers than non-smokers. Coronary risk factors of newcomers were not different from that of the stayers at follow-up except for slightly, but not significantly, higher smoking rates in newcomers. These findings suggest that drop-out and newcomer bias need to be assessed and its effect studied before final evaluation of data in community follow-up studies.