In general, in a randomized clinical trial, it is necessary to determine if any baseline differences between groups may have affected results. We were not able to assess the success of randomization because, other than mean age, the authors did not provide baseline data for the treatment groups. Important demographic variables to consider include age distribution, sex, income, and maternal education level. Baseline information on other variables known to affect rates of acute respiratory illness (day-care attendance, passive exposure to cigarette smoke, history of atopy, and breastfeeding) is also critical. This information is important because differences between groups could have confounded results. Confounding can occur when an extrinsic factor is associated with both the predictor and outcome variables.4 It is then difficult to determine if the extrinsic factor itself caused the observed effect. For example, confounding could occur if a relatively larger proportion of children in the placebo group attended day care. The placebo group might have had more illness episodes because of day-care attendance rather than it being a true reflection of the efficacy of Chizukit. Although in this study baseline variables should have been roughly balanced between the 2 groups because of careful randomization, lack of information comparing treatment groups at entry renders the results difficult to evaluate.