Does the double-blind method work? Many medical trials randomly assign pa-

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tients to either an active treatment or a placebo. These trials are always doubleblind.

Sometimes the patients can tell whether or not they are getting the active treatment. This defeats the purpose of blinding. Reports of medical research usually ignore this problem. Investigators looked at a random sample of 97 articles reporting on placebo-controlled randomized trials in the top five general medical journals. Only 7 of the 97 discussed the success of blinding—and in 5 of these the blinding was imperfect.26 What proportion of all such studies discuss the success of blinding? (Use 95% confidence.)