title: The impact of deployment experience and prior healthcare utilization on enrollment in a large military cohort study.
abstract: BACKGROUND
  Longitudinal cohort studies are highly valued in epidemiologic research for their ability to establish exposure-disease associations through known temporal sequences. A major challenge in cohort studies is recruiting individuals representative of the targeted sample population to ensure the generalizability of the study's findings.
  
  
  METHODS
  We evaluated nearly 350,000 invited subjects (from 2004-2008) of the Millennium Cohort Study, a prospective cohort study of the health of US military personnel, for factors prior to invitation associated with study enrollment. Multivariable logistic regression was utilized, adjusting for demographic and other confounders, to determine the associations between both deployment experience and prior healthcare utilization with enrollment into the study.
  
  
  RESULTS
  Study enrollment was significantly greater among those who deployed prior to and/or during the enrollment cycles or had at least one outpatient visit in the 12 months prior to invitation. Mental disorders and hospitalization for more than two days within the past year were associated with reduced odds of enrollment.
  
  
  CONCLUSIONS
  These findings suggest differential enrollment by deployment experience and health status, and may help guide recruitment efforts in future studies.
authors.affiliation: Deployment Health Research Department, Naval Health Research Center, 140 Sylvester Rd, San Diego, CA 92106, USA. jaime.horton@med.navy.mil
authors.forename: Jaime L
authors.initials: JL
authors.lastname: Horton
authors.forename: Isabel G
authors.initials: IG
authors.lastname: Jacobson
authors.forename: Alyson J
authors.initials: AJ
authors.lastname: Littman
authors.forename: John E
authors.initials: JE
authors.lastname: Alcaraz
authors.forename: Besa
authors.initials: B
authors.lastname: Smith
authors.forename: Nancy F
authors.initials: NF
authors.lastname: Crum-Cianflone
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D003695:Delivery of Health Care / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D008889:Military Personnel / Q000706:statistics & numerical data; D010342:Patient Acceptance of Health Care; D018579:Patient Selection; D011446:Prospective Studies; D045808:Refusal to Participate; D014857:Warfare; D055815:Young Adult