Practice of Epidemiology The Healthy Worker Effect in Cancer Incidence Studies

Use of the general population as a reference might cause serious underestimation of the risk of cancer in working populations because of the healthy worker effect. Using incidence rates, we studied how this underesti-mation varied according to subtypes of cancer by comparing a large cohort of randomly selected Norwegian workers hired between 1981 and 2003 (n = 366,114) with the general Norwegian population. The cohort was linked to the Cancer Registry of Norway, including all new cancer cases (n = 11,271) reported up to 2003. We found marked potential for the healthy worker effect for overall cancer incidence in male workers (standardized incidence ratio (SIR) = 0.91, 95 % confidence interval: 0.89, 0.93) but not in female workers (SIR = 0.99, 95 % confi-dence interval: 0.95, 1.03). A statistically significantly lower incidence was found among men for cancers of th