Doctors were told last month that we should stop doing so many screenings for prostate cancer with the prostate-specific antigen test. We learned that sigmoidoscopy is a cheaper, easier and effective alternative to colonoscopy for colon cancer screening. And a study I led turned up strong evidence that routine lung cancer screenings are justified only for people at high risk because of heavy smoking in the past. Regular mammograms aren’t necessary for women in their 40s and are needed only every two years for women ages 50 to 74, the United States Preventive Services Task Force has decided. For many women, Pap smears are required only every three years, not every year, the group also says now. This deluge of do-less recommendations results from research into tests and procedures that have been arguably overused. You’d think these pronouncements would bring a sea change in the way patients are treated in this country. But my guess is that little will change. Many doctors, maybe most, will ignore these findings and keep doing what they have been doing all along.