Assessing nonresponse bias at follow-up in a large prospective cohort of relatively young and mobile military service members
1 Seattle Epidemiologic Research and Information Center, Department of Veterans Affairs Puget Sound Health Care System, Seattle, WA, USA
2 Department of Epidemiology, University of Washington, Seattle, WA, USA
3 Department of Deployment Health Research, Naval Health Research Center, San Diego, CA
4 Analytic Services, Inc. (ANSER), Arlington, VA, USA
5 Departments of Preventive Medicine and Biometrics, Uniformed Services University of Health Sciences, Bethesda, MD, USA
6 Madigan Army Medical Center, Fort Lewis, WA, USA
BMC Medical Research Methodology 2010, 10:99 doi:10.1186/1471-2288-10-99Published: 21 October 2010
Nonresponse bias in a longitudinal study could affect the magnitude and direction of measures of association. We identified sociodemographic, behavioral, military, and health-related predictors of response to the first follow-up questionnaire in a large military cohort and assessed the extent to which nonresponse biased measures of association.
Data are from the baseline and first follow-up survey of the Millennium Cohort Study. Seventy-six thousand, seven hundred and seventy-five eligible individuals completed the baseline survey and were presumed alive at the time of follow-up; of these, 54,960 (71.6%) completed the first follow-up survey. Logistic regression models were used to calculate inverse probability weights using propensity scores.
Characteristics associated with a greater probability of response included female gender, older age, higher education level, officer rank, active-duty status, and a self-reported history of military exposures. Ever smokers, those with a history of chronic alcohol consumption or a major depressive disorder, and those separated from the military at follow-up had a lower probability of response. Nonresponse to the follow-up questionnaire did not result in appreciable bias; bias was greatest in subgroups with small numbers.
These findings suggest that prospective analyses from this cohort are not substantially biased by non-response at the first follow-up assessment.