Comparison of measurement strategies for prospective occupational epidemiology

In the context of a prospective assessment of exposure for epidemiology, our objective is to obtain an optimal group-based design of allocation of a fixed total number of measurements. Such a design has been described by Ashford [Ashford JR. (1958) The design of a long-term sampling programme to measure the hazard associated with an industrial environment. J R Statist Soc A; 121: 331-47]. As this strategy is not operational, we developed three series of strategies: the first based on simplifications of Ashford's strategy; the second based on a pilot study; and the third on an iterative assessment of the group specific standard deviation of exposure. These strategies are compared by simulating a day-to-day individual exposure in several industrial sites and the resulting health effect. Our criteria for comparing strategies are the mean squared error of the estimated exposure in each group weighted by the number of subjects and the mean squared error of the estimated linear regression coefficient in the dose-response relationship. Strategies relying on an iterative approach have been found to perform best whatever the circumstances, nearly as well as Ashford's optimal strategy.