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Open Access Research article

Assessing nonresponse bias at follow-up in a large prospective cohort of relatively young and mobile military service members

Alyson J Littman12*, Edward J Boyko1, Isabel G Jacobson3, Jaime Horton3, Gary D Gackstetter4, Besa Smith3, Tomoko Hooper5, Timothy S Wells3, Paul J Amoroso6, Tyler C Smith3 and the Millennium Cohort Study

Author Affiliations

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

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BMC Medical Research Methodology 2010, 10:99  doi:10.1186/1471-2288-10-99

Published: 21 October 2010

Abstract

Background

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.

Methods

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.

Results

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.

Conclusions

These findings suggest that prospective analyses from this cohort are not substantially biased by non-response at the first follow-up assessment.