Editor—Thornton et al say that claims for the reduction in relative risk of death from breast cancer among women who are screened have ranged from 63% to 6%.1 This is crucial information for women considering attending. Unfortunately the lower limit, attributed to our paper in the BMJ in 2000,2 is no such estimate. The 6% refers to the reduction seen in death rates from breast cancer for invited women (including those screened and non-attenders) in 1998, from a programme that started between 1988 and 1995.
For reasons we explained in great detail in our paper (including the fact that many deaths in the 1990s will have been women with a diagnosis of breast cancer before any invitation to screening), this is most likely to estimate the beginnings of an effect—not the full effect. It is therefore inaccurate and extremely unhelpful to quote this figure to women as an estimated relative risk reduction from attending screening—it is not.
Competing interests: None declared.
References
- 1.Thornton H, Edwards A, Baum M. Women need better information about routine mammography. BMJ 2003;327: 101-3. (12 July.) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Blanks RG, Moss SM, McGahan CE, Quinn MJ, Babb PJ. Effect of NHS breast screening programme on mortality from breast cancer in England and Wales, 1996-8: comparison of observed with predicted mortality. BMJ 2000;321: 665-9. [DOI] [PMC free article] [PubMed] [Google Scholar]