title: Effects of self-reported health conditions and pesticide exposures on probability of follow-up in a prospective cohort study.
abstract: BACKGROUND
  We investigated the potential for selection bias due to non-participation in the follow-up of a large prospective cohort study.
  
  
  METHODS
  Licensed pesticide applicators (52,395 private; 4,916 commercial) in the Agricultural Health Study provided demographic, health, and pesticide exposure information at enrollment (1993-1997) and in a 5-year follow-up telephone interview. Factors associated with non-participation in the follow-up were identified using multiple logistic regression. Potential for selection bias was evaluated by comparing exposure-disease associations between the entire cohort and the follow-up subset.
  
  
  RESULTS
  Sixty-six percent of private and 60% of commercial applicators completed the follow-up interview. Private and commercial applicators who did not complete the follow-up reported at enrollment younger age, less education, lower body mass index, poorer health behaviors but fewer health conditions, and lower pesticide use. Estimates of exposure-disease associations calculated with and without non-participants did not indicate strong selection bias.
  
  
  CONCLUSIONS
  Differences between non-participants and participants in the follow-up interview were generally small, and we did not find significant evidence of selection bias. However, the extent of bias may depend on the specific exposure and outcome under study.
authors.affiliation: Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Martha P
authors.initials: MP
authors.lastname: Montgomery
authors.forename: Freya
authors.initials: F
authors.lastname: Kamel
authors.forename: Jane A
authors.initials: JA
authors.lastname: Hoppin
authors.forename: Laura E
authors.initials: LE
authors.lastname: Beane Freeman
authors.forename: Michael C R
authors.initials: MC
authors.lastname: Alavanja
authors.forename: Dale P
authors.initials: DP
authors.lastname: Sandler
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000383:Agriculture; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D007484:Iowa / Q000453:epidemiology; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009657:North Carolina / Q000453:epidemiology; D009784:Occupational Diseases / Q000453:epidemiology* / Q000209:etiology; D016273:Occupational Exposure / Q000009:adverse effects*; D016017:Odds Ratio; D010342:Patient Acceptance of Health Care; D010575:Pesticides / Q000633:toxicity*; D011336:Probability; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D015983:Selection Bias; D011795:Surveys and Questionnaires; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D010575:Pesticides