[Which controls should be chosen in a case-control study? Survey of bladder cancer in Hérault]

A case-control investigation about bladder cancer was carried out in Herault department with 219 incident cases from January 1987 to May 1989 and two control groups: 196 hospital controls randomized from hospital admission lists and 794 population controls randomized from census data. According to the comparison for those two groups, there are few socio-demographic differences; but hospital controls are more exposed to smoking, coffee, alcohol, artificial sweetners. So, the odds ratios with those hospital controls are under-estimated. We can evaluate the resulting biais.