Research article
Determinants of subject visit participation in a prospective cohort study of HTLV infection
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* Corresponding author: Deborah A DeVita devitad@labmed2.ucsf.edu
1 Department of Laboratory Medicine, University of California, San Francisco, California, USA
2 Community Health Systems, School of Nursing, University of California, San Francisco, California, USA
3 Blood Systems Research Institute, San Francisco, California, USA
BMC Medical Research Methodology 2009, 9:19 doi:10.1186/1471-2288-9-19
Published: 10 March 2009Abstract
Background
Understanding participation in a prospective study is crucial to maintaining and improving retention rates. In 1990–92, following attempted blood donation at five blood centers, we enrolled 155 HTLV-I, 387 HTLV-II and 799 HTLV seronegative persons in a long-term prospective cohort.
Methods
Health questionnaires and physical exams were administered at enrollment and 2-year intervals through 2004. To examine factors influencing attendance at study visits of the cohort participants we calculated odds ratios (ORs) with generalized estimated equations (GEE) to analyze fixed and time-varying predictors of study visit participation.
Results
There were significant independent associations between better visit attendance and female gender (OR = 1.31), graduate education (OR = 1.86) and income > $75,000 (OR = 2.68). Participants at two centers (OR = 0.47, 0.67) and of Black race/ethnicity (OR = 0.61) were less likely to continue. Higher subject reimbursement for interview was associated with better visit attendance (OR = 1.84 for $25 vs. $10). None of the health related variables (HTLV status, perceived health status and referral to specialty diagnostic exam for potential adverse health outcomes) significantly affected participation after controlling for demographic variables.
Conclusion
Increasing and maintaining participation by minority and lower socioeconomic status participants is an ongoing challenge in the study of chronic disease outcomes. Future studies should include methods to evaluate attrition and retention, in addition to primary study outcomes, including qualitative analysis of reasons for participation or withdrawal.