The second methodological issue that we would like to draw attention to involves the concept of “overadjustment,” which we believe occurred in this study. Overadjustment is a condition whereby statistical adjustment is inadvertently carried out for a variable that is either in the causal pathway between the exposure and the outcome (an intermediate cause), or is strongly related to either the exposure (multicollinearity) or the outcome.3–5 In this particular study, “altered mental state,” which is clearly a strong predictor for TFAD of > 4 h, was also a potent predictor for mortality. Meanwhile, TFAD of > 4 h was a predictor for mortality in univariate analysis but was not found to be so after multivariate analysis (see Table 3 in the article by Waterer et al1). Here, we cannot rule out the possibility that the variables altered mental status, TFAD of > 4 h, and mortality are all are on a causal pathway, with altered mental status resulting in a TFAD of > 4 h, and a TFAD of > 4 h leading to increased mortality. Overadjustment may have occurred when the authors inappropriately incorporated factors predicting TFAD, together with TFAD, in the multivariate analysis for predicting mortality. An alternative analytic approach that would help to clarify this relationship would be to perform a stratified multivariate analysis (for those with and without altered mental status) evaluating whether TFAD of > 4 h is associated with mortality.