Cytologic screening for cervix cancer: each year or each 3 years?

Screening is the systematic proposal of a medical procedure to a defined population at a defined interval. The efficacy and effectiveness of screening can only be demonstrated by a decreased mortality (not lethality) in case-control studies or randomised prospective studies. For cervix cancer, the only test with a decreased mortality proven by case-control studies (since 1979 only) is the cervix cytologic screening or 'Pap' smear. Systematic proposal is proven to be optimal every three years, no further gain being demonstrated for annual or biennial screening.