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To the Editor: The article by Dr McAlister and colleagues¹ raises some interesting issues in evaluating clinical trials of drug efficacy. Although we agree that the best evidence for efficacy comes from head-to-head randomized controlled trials (RCTs), we think that observational studies can provide valuable results in a comparison of drugs and that this class of study should not merit the lowest weight. McAlister et al may be unaware of new developments in design, such as case-crossover studies² and the use of propensity scores,³ which overcome some of the threats to validity. In fact, the whole purpose of propensity scores is to put observational data into an RCT framework. Moreover, we think that direct comparisons of clinical outcomes should carry more weight than the use of surrogate measures. For example, the effect of statins in preventing cardiovascular events may be due to improving lipid profiles or lowering of blood pressure . . . [Full Text of this Article]

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