It’s not an accident that evidence based guidelines more or less began with clinical preventive services. Unlike treatment for problems that produce symptoms, preventive medicine is optional. We have the luxury of time to gather and evaluate the evidence for the efficacy and even effectiveness of screening tests and counselling. When someone rushes into your surgery bleeding or doubled over in pain, it would hardly be acceptable to send them away untreated to await the results of a randomised controlled trial for their problem. But that is just what we do when people want to know whether they should undergo computed tomography to screen for lung cancer or be given vitamins to prevent heart disease. “Sorry,” we say, “insufficient evidence.”

And this is even truer for children—at least when the question is whether to screen them for early signs or symptoms of adult diseases. Firstly, we need to know whether the problem will even persist into adulthood. Secondly, do we have a safe and effective treatment? And most importantly, does treating the …