“Be not the first by whom the new is tried/ nor yet the last to cast the old aside” is a well known medical adage, though it is a slight misquotation from An Essay on criticism by Alexander Pope (1711), who was talking about the use of new words rather than clinical procedures. Readers of this journal do want to be the first to try things, provided there is good evidence. But what if the evidence is suggestive rather than definitive? For example, a Cochrane review of compression stockings for preventing deep vein thrombosis(DVT) in airline passengers (2006;CD004002) finds that there is good evidence that they prevent symptomless DVT but could not find evidence that they prevent death, pulmonary embolism, or even symptomatic DVT, because, contrary to popular belief, such events are rare in long distance air travellers. So I guess my advice would be “wear them if flying worries you.” But say that the person about to fly is a nervous doctor who then asks to be tested for thrombophilic genetic polymorphisms, which are present in 30% of the population. I think here the answer is a definite no. Even if he …