The review of placebo controlled trials of sodium cromoglycate (SCG) in childhood asthma by Tasche et al 1 concludes that “there is insufficient evidence that SCG has a beneficial effect as maintenance treatment in children with asthma”.

We do not believe this conclusion is justified. The principal criteria for assessing the efficacy of inhaled SCG are the mean differences in the effect on the symptoms of cough and wheeze between SCG and placebo across all trials included in the review. The 95% confidence intervals for these differences are 0.12 to 0.27 for cough and 0.11 to 0.26 for wheeze. As the differences are in favour of SCG and the confidence intervals do not include zero, the only conclusion that can be drawn is that there is strong statistical evidence for a beneficial effect of SCG in children with asthma—the reverse conclusion to that presented.

The review identified 24 randomised controlled trials and is claimed to include “all published randomised, placebo controlled trials”. Two published trials are not included (those by Bermanet al 2 and Mikawaet al 3) and the trial by Silverman et al,4 which is included, does not meet the author's criteria. Both excluded trials, which involved 472 children, reported statistically significant differences in favour of SCG compared with placebo. The study by Silverman et al compared the combination of inhaled SCG and isoprenaline with isoprenaline alone and did not include a placebo comparison.

The authors have calculated a tolerance distribution for study effects and we believe it is this distribution which has been fundamentally misinterpreted. They provide a tolerance interval for the results of future studies based on the between study variation seen. The fact that this interval contains zero does not mean that there is no evidence of a difference between treatments, as …