Clinicians who offer screening tests bear a heavier responsibility than those consulted by people who are, or believe themselves to be, ill. Most people who accept the offer derive no benefit because they are true negatives while the false positives and false negatives are harmed in the process. This dilemma is made clear by David Eddy in a classic introductory chapter to the American College of Physicians’ update to their 1991 bestseller “Common Screening tests.” The new book contains 5 United States Preventive Services Task Force (USPTF) reviews of screening programmes that were published in the Annals of Internal Medicine (type 2 diabetes, postmenopausal osteoporosis, breast cancer, colorectal cancer, …