First of all, the mortality reduction possible with screening depends on what kinds of studies you look at.
There's one kind of research called a randomized trial, where you have a control group and a study group. Then there's observational data. Screening has been under way in Canada since 1988. We know from observational data—not randomized trial data—that women in their forties are 44% less likely to die of breast cancer if they have screening. If you rely just on the randomized trials, which are now 40 to 60 years old.... They were done at a time when mammograms were X-ray film that we read on a light box. Now they're done digitally on computers with lots of enhancements that make them more accurate. If you look at just the randomized trials, the mortality reduction was only between 15% and 20%.
The task force this time included observational studies in addition to the randomized trials, using the grade system you heard about earlier. What they did is prioritize the older studies and downgrade the importance of the observational studies. In fact, if you look at all the observational studies, not just the Canadian one, you'll find that the mortality reduction from mammography alone is in the range of 53% fewer deaths. Yet, because of the task force's overemphasis on anxiety from recalls and overdiagnosis, they concluded that the harms of screening outweigh the benefits.