Healthy Skepticism Library item: 19027

Warning: This library includes all items relevant to health product marketing that we are aware of regardless of quality. Often we do not agree with all or part of the contents.

Publication type: Journal Article

Barry DA, Baines CJ, Baum M, Dickersin K, Fletcher SW, Gøtzsche PC, Jørgensen KJ, Junod B, Maehlen J, Schwartz LM, Welch HG, Woloshin S, Thornton H, Zahl PH.
Flawed inferences about screening mammography's benefit based on observational data.
J Clin Oncol 2009 1; 27:(4):639-40
http://jco.ascopubs.org/content/27/4/639.long

Abstract:

A recent article by Badgwell et al1 finds that among breast cancer patients at least 80 years of age, the 5-year breast cancer–specific survival was 82% among women who were nonusers of screening mammography, as opposed to 88% among those who were irregular users of screening and 94% among regular users. The investigators are cautious about the implications of this observation: “Our findings add to the accumulating evidence that the use of regular mammography may be beneficial for older women.”1(p6) However, they are not cautious enough. Observations such as theirs are expected with any screening program and cannot address benefit.

The authors point out that their study was subject to a healthy-person bias. While true, the real culprits are lead-time and length biases, which they do not mention. These biases are elementary and fundamental in cancer epidemiology. But they seem to have been unknown also to the Journal’s editors who handled the manuscript—had they understood them, they could not have accepted the manuscript for publication. …