Article included in edition Volume IV :: Nr.2 :: December 2008

Could You Repeat That?

The measurement of the impact of work on health: we need longitudinal studies, but which ones?

Thomas Coutrot1 & Loup Wolff2
(1) Direction de l’Animation de la Recherche,
des Etudes et des Statistiques (DARES)
39-43, quai André Citroën — 75015, Paris
thomas.coutrot@dares.travail.gouv.fr
(2) Direction de l’Animation de la Recherche,
des Etudes et des Statistiques (DARES)
39-43, quai André Citroën — 75015, Paris
loup.wolff@dares.travail.gouv.fr
Abstract

This paper intends to present a systematic comparison between the performances of “naive” epidemiological models, explaining the prevalence of health issues through existing characteristics of workers, and more rigorous models that include a history of some former professional exposures (retrospective statistical models), or models that study the incidence (instead of the prevalence) of the disorders, according to either the exposure from the initial date (longitudinal standard models), or the evolution of the exposure (dynamic models). We first show the weakness of considering the impact of individual misleading factors such as the consumption of alcohol and tobacco, living conditions or medical history. However, the correlations between health and employment characteristics highlighted by the naive models remain practically unmodified in the more thorough models. That does not mean that these factors have no effects on health. On the contrary, the analysis shows the importance of some of these effects. But the effects of the professional factors and of the personal ones act independently. We then examine the respective merits of “standard” and “dynamic” models. The first ones explain the incidence of health disorders by exposure between two dates with reference to the initial date. The second ones take the evolution of the exposure between the two dates as explanatory variables. Concerning the (infra)pathologies related to stress, the “standard” models appear under-efficient, insofar as they clearly underestimate the impact of exposures on health disorders. This lack of efficiency is probably due to the greater reversibility of disorders in the case of the disappearance of exposure, a phenomenon that the “standard” model confuses with a negative correlation between the exposure and the disorder.

Keywords statistical models in epidemiology, health and working conditions, individual factors of confusion.