Effects of smog on absenteeism in forestry workers

Absenteeism among 161 Dutch forestry workers was investigated in a cohort study. The rate of taking sick leave was related to the concentrations of sulfate and ozone in ambient air, the air temperature, and the relative humidity. The incidence of absenteeism was treated as a Poisson process, with the size of population at risk as the offset factor and with the environmental monitoring data as hazard factors. There appeared to be some overdispersion; therefore, in a second analysis the incidence of absenteeism was also treated as a negative binomial outcome. With the exception of a separate overdispersion parameter in the negative binomial approach, both methods yielded approximately the same results. Although no significant association was found between absence rate and the measured ambient-air-quality data, there appeared to be a time lag of 3 d between a peak in temperature and 1 d in absenteeism.