[Effectiveness of screening for cervical cancer in Taiwan. A case-control study].

The cervical cancer screening program in Taiwan was carried out in two phases. This study was based on the Phase II data from April 1, 1979, through June 30, 1984. There were 56 completed data cases of invasive cervical cancer. The purposes of this case-control study was: (1) to estimate an exposure odds ratio; (2) to estimate the prevented fraction (PF), proportion of potential cases that were actually prevented by the Pap smear test in the screened population; and (3) to study factors related to the effectiveness of screening. The protective effect of a previous Pap test was not shown between cases and controls in this study. The PFs were 6% for the screened population and 20% for those having had a previous Pap test. No significant protected effect of a previous Pap test was found in this study, whether in univariate analysis or logistic regression. Possible explanations are: (1) incomplete follow-up for those women with abnormal smears; (2) high false negative rate due to laboratory error, or poor technique in smear taking; (3) infrequent screening with too long a screening interval; (4) low coverage rate of a Pap test; and (5) selection bias.