A PSA test can reveal the presence of prostate cancer. But not all such cancers are fatal and treatment involves the risk of impotence. Do you really want the test? It’s difficult for patients to evaluate these kinds of risks. Mahalanobis points us to an article advocating visual tools such as roulette wheels to help patients understand relative risks and chance. Even better than the diagrams is this impressive video; the video may be of independent interest to the older men in the audience.