To the Editor Harding et al1 use ecological analysis to assess an important and complex issue. The authors would judge mammography outcomes but lack key information to draw reliable conclusions. They do not know which women actually had mammograms or which cancers were detected by screening. The report relies on self-reporting of mammography, the accuracy of which is questionable. They assume fairly uniform populations, which is unlikely. Lacking longitudinal data, the authors have no idea whether the rate of advanced cancers declined. In fact, there are numerous confounding factors that could make their analysis irrelevant.
Monticciolo D, Morris E. Unreliable Conclusions of Breast Cancer Screening, Incidence, and Mortality. JAMA Intern Med. 2016;176(1):140-141. doi:10.1001/jamainternmed.2015.7204