Assessing nonresponse bias at follow-up in a large prospective cohort of relatively young and mobile military service members.
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.
Littman
Alyson J
AJ
Seattle Epidemiologic Research and Information Center, Department of Veterans Affairs Puget Sound Health Care System, Seattle, WA, USA. alyson@u.washington.edu
Boyko
Edward J
EJ
Jacobson
Isabel G
IG
Horton
Jaime
J
Gackstetter
Gary D
GD
Smith
Besa
B
Hooper
Tomoko
T
Wells
Timothy S
TS
Amoroso
Paul J
PJ
Smith
Tyler C
TC
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000437:Alcoholism; D015982:Bias; D015331:Cohort Studies; D003865:Major Depressive Disorder; D004522:Educational Status; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D008889:Military Personnel / Q000523:psychology; D012737:Sex Factors; D012907:Smoking; D011795:Surveys and Questionnaires; D055815:Young Adult