It's hard to know what works

Papers p 1041

The tenet that clinical practice should be guided by rigorous evidence has become so ingrained that clinicians who are slow on the uptake are seen as not aware of the evidence, bogged down by tradition, or—worse—having selfish motives for ignoring evidence. Rarely is the evidence itself questioned. Yet, if evidence were a straightforward concept, there would be no reason for the two disciplines that appear to be governed by it, law and medicine, to be at loggerheads so often.

The evidence available does not necessarily reveal what you are interested in for a particular situation. Thus many reviews in the CochraneLibrary, the gold standard of systematic reviews, devote no attention to adverse effects in assessing the effectiveness of health care interventions (Bastian H, Middleton P. Cochrane Colloquium,Amsterdam, 1997). Yet any intervention (be it advice, screening for disease,drugs, or surgery) that is likely to be beneficial for some people is also likely to harm others. Even if the evidence is clear on the effectiveness of an approach, it does not necessarily reveal how to pursue that approach.For example, systematic reviews may show …