With great interest we have read the article by Douglas A. Colquhoun et al. regarding the effect of lower tidal volume ventilation on postoperative pulmonary complication in patients undergoing lung resection surgery with one-lung ventilation. There are two important points of concern.

First, an a priori test was used to calculate the sample size by using a two-sided Z test with unpooled variance, and the results showed that 1,315 unmatched cases in each group (total study N = 2,630) provided 90% power at an alpha = 0.05 to detect a 5% difference. However, the Z test was used to calculate the sample size, whereas the conditional logistic regression model was used to analyze the relationship of protective ventilation and pulmonary complication (main outcome), and only 762 patients matched were enrolled in the logistic regression. We think that...

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