Abstract : Abstract : Quality of life is a central concern in medicine.Thus estimation of the number of years of life free of some disease lost due to an occupational exposure is frequently required. The amount of compensation due to the worker relies upon this estimation.
The motivating example is a French case-control study on the occurrence of lung cancer for workers exposed to asbestos (J.C. Pairon et al, 2009). We adapt to case-control study the threshold regression (TR) model, also named first hitting time model (FHT), which was initially developed for cohort studies. This model allows us to treat the occupational exposure as an accelerator of the time to onset of the disease, while the other covariates are divided into two classes, acting differently on the time to onset: the built-in ones (like genetic factors for example) and the lifelong ones (like tobacco consumption for example).
The first hitting time model developed by M.-L. T. Lee and G. A. Whitmore, 2006 , 2010, enables us to separate the covariates into three different kinds : first the initial covariates, like sex, past family disease history, genetic factors, that act on the initial amount of health of the subject. Then the lifelong covariates, like biological and environmental covariates that act on (or account for) the decrease of the initial amount of health. It may include for example cholesterol level and tobacco consumption. Finally the occupational exposure under study may accelerate the time to onset of the considered disease.
The number of years lost due to occupational exposure to asbestos is then derived from the model by replacing for each exposed subject his time to onset by the decelerated time he would have had when exposure is removed and all other factors in the model remain the same.