One of the disadvantages of our analysis was that there was some heterogeneity in the outcome set in the studies chosen for review; thus, some outcomes which we did not select were unable to be included within the pooled analysis. For example, in the study by Bisgaard et al. , we could not compare USMAs, because in this study, they compared the proportion of patients who had at least one USMA rather than the number of unscheduled visits (37% for montelukast; 42% for placebo).