Not too many studies present their data also in the form of numbers needed to treat (NNT) or harm (NNH). The reason for that is that there is a debate over the importance and value of such a mode of analysis. Recently, two major studies included a calculation of the NNT, which may serve as an opening point for discussing this issue. A long-term, Swedish cohort examined the effect of mammographic screening on breast cancer mortality during a 29-year follow-up period . Over 133,000 women aged 40–74 years were randomized either into a group invited to mammographic screening or a control group receiving the usual care. The traditional presentation of results pointed at a highly significant decrease in breast cancer mortality in the invited-for-mammography group (relative risk 0.69; 95% confidence interval (CI) 0.56–0.84; [i]p[/i] < 0.0001). This translated into the figure of 414 women who had to undergo screening for 7 years in order to prevent one breast cancer death . In the Women’s Health Initiative observational study , 25,448 postmenopausal women aged 50–79 years who underwent either bilateral salpingo-oophorectomy (BSO) or hysterectomy with ovarian conservation were followed for 7.6 years. It was found that removal of the ovaries saved one ovarian cancer in 323 women with BSO compared with those whose ovaries were left intact during hysterectomy .
Department of Medicine T, Ichilov Hospital, Tel-Aviv, Israel
Department of Public Health and Family Medicine, University of Cape Town, South Africa
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