The first study (Study I) was a population-based case-control study including 21 sites of cancers conducted between 1979 and 1986. Cases were histologically confirmed and were restricted to males aged between 35 and 70 years.
Population controls were selected from electoral lists and frequency matched by age. The response rates among eligible subjects were 79 % among cases and 72 % among controls. From Study I, 857 male lung cancer cases and 533 male controls were available for these analyses.