Effects of self-reported health conditions and pesticide exposures on probability of follow-up in a prospective cohort study.
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.
Montgomery
Martha P
MP
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.
Kamel
Freya
F
Hoppin
Jane A
JA
Beane Freeman
Laura E
LE
Alavanja
Michael C R
MC
Sandler
Dale P
DP
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
D010575:Pesticides