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To the Editor: Dr Balk and colleagues¹ found that randomized controlled trials (RCTs) with high scores for allocation concealment, double-blinding, and 22 other quality measures had similar results as low-quality trials, as defined by these indicators. However, the authors' ambitious efforts may have diluted the quality of some their assessments and hindered comparability with prior studies.

Most notably, Balk et al defined allocation concealment differently than in the studies they apparently wanted to replicate. First, in their definition, opaque envelopes constituted adequate allocation concealment whereas in earlier studies of trial quality, envelopes had to be described as serially numbered, sealed, and opaque.^2-4 This may seem a minor point, but because envelopes are the most commonly reported approach, a minor definitional deviation can have major effects. In one study, about half of authors reported using an envelope method (of those reporting any allocation concealment mechanism), but less than a quarter of . . . [Full Text of this Article]

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