The population with official residence in the catchment area represented the study pool from which controls were sampled. The Regional Health Service (RHS) database contains information on subjects' demographics and on the family physician for virtually all Italians. We sampled population controls from updated population databases obtained periodically (twice a year) from the Lombardy Region; the age of controls was calculated as of pre-specified dates, i.e., July 22nd and January 22nd of each year. Controls were selected randomly within 90 cells (see below) to yield a set of controls with a distribution that initially approximated the case distribution based on year 2000 lung cancer admissions, and subsequently was based on enrolled EAGLE lung cancer cases, for 3 key variables: residence (5 areas: Brescia, Milan, Monza, Pavia, Varese), gender, and five-year age classes in the range 35–79 years (5 × 2 × 9 combinations of residence-gender-age categories). To select controls, a random number was assigned to each subject using statistical software, and the records were sorted based on this random number. Each subject with a number below the target enrollment number
