title: Controlling for time-since-hire in occupational studies using internal comparisons and cumulative exposure.
abstract: Employees within an occupational cohort may demonstrate a more favorable mortality experience while maintaining employment than those who leave employment. At the same time, they may experience an apparent decline in health with time-since-hire. The time-since-hire effect may occur independently of exposure but may nevertheless result in groups categorized by cumulative exposure that are not comparable. Controlling for time-since-hire appears to solve this problem. To quantify the empirical bias in estimates of exposure effect due to confounding from time-since-hire, we analyzed two occupational cohorts using Poisson regression with and without adjustment for time-since-hire or time-since-start-of-follow-up. In a cohort exposed to airborne arsenic, a strong dose-response relation with respiratory cancer mortality had been established. In a cohort exposed to external, penetrating ionizing radiation, a weak and controversial dose-response relation had been reported. The parameter estimates relating exposure to disease from the models that explicitly adjusted for time-since-hire or time-since-start-of-follow-up are within 10% of the estimates from models that did not. It appears, from this empirical analysis of two datasets, that occupational studies may not need to adjust explicitly for such time-related factors as time-since-hire or time-since-start-of-follow-up if these are implicitly controlled through other variables in the model.
authors.affiliation: Department of Epidemiology, School of Public Health, University of North Carolina, Chapel Hill, USA.
authors.forename: H M
authors.initials: HM
authors.lastname: Arrighi
authors.forename: I
authors.initials: I
authors.lastname: Hertz-Picciotto
mesh_terms: D001151:Arsenic / Q000009:adverse effects; D015982:Bias; D015331:Cohort Studies; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D015994:Incidence; D016014:Linear Models; D008297:Male; D009784:Occupational Diseases / Q000453:epidemiology* / Q000209:etiology; D016273:Occupational Exposure / Q000009:adverse effects / Q000706:statistics & numerical data*; D016012:Poisson Distribution; D011839:Radiation, Ionizing; D012142:Respiratory Tract Neoplasms / Q000453:epidemiology* / Q000209:etiology; D018570:Risk Assessment; D015996:Survival Rate; D013997:Time Factors
chemical_list: D001151:Arsenic