Incidence density matching with a simple SAS computer program.

Incidence density matching is the method of choice for selecting controls in nested case-control studies, but its use has been limited by its computational complexity. We describe incidence density matching in nested case-control studies with a simple and flexible SAS computer program. The program contains no restrictions on the number of matching factors, although it is usually only necessary to match on age (in incidence density fashion) and on gender. The program is illustrated with data from an historical cohort study of the mortality experience of workers at an asbestos textile manufacturing plant.