Misconceptions about efficacy of mammography screening: a public health dilemma.

OBJECTIVE: This study assessed accuracy of women's opinions about reduction in mortality from breast cancer attributable to mammography screening. DESIGN: Cross sectional survey. SETTING: General population of Geneva, Switzerland. PARTICIPANTS: 895 randomly selected women aged 40 to 80 years, free of breast cancer. RESULTS: Women estimated the proportion of deaths from breast cancer that regular mammography screening prevents in women over age 50. Only 19.3% of the respondents assessed screening efficacy realistically (that is, reduction by about one fourth); 52.0% overestimated efficacy; 26.0% "didn't know", and 2.6% stated that screening prevents no death. Women who believed mammography screening to be effective had more positive attitudes toward screening (higher scores of pros and lower scores of cons) and were more likely to plan to have a mammogram (both p<0.001). Lack of opinion about the benefit of mammography screening was more common among women who had not consulted a gynaecologist recently (p=0.02) nor had had a mammogram during the past two years (p=0.009), who had no opinion about their risk of breast cancer (p<0.001), and who were 70 to 80 years old (p=0.04). Compared with women who provided realistic estimates of screening efficacy, those who overestimated efficacy believed to be at higher risk of breast cancer than other women (p=0.04) and were more likely to be Swiss nationals (p=0.001). CONCLUSIONS: Most women overestimated and many were uninformed about the efficacy of mammography screening. Therefore, few women were able to take truly informed decisions about screening mammography.