LETTERS TO THE EDITOR Inhaled sodium cromoglycate

The systematic review and meta-analysis performed by Tasche and colleagues appears to have been carried out with commendable thoroughness. The results seem clear cut: sodium cromoglycate is ineVective as maintenance therapy in children with asthma. However, their conclusions are not objective but depend in the final analysis on their multivariate regression model. Perhaps this is where the most important bias has crept into the analysis. As in the case of many new drugs, clinical trials are first carried out in adults, later in schoolchildren, and finally (if ever) in infants and pre-schoolchildren. This appears to have been the case with sodium cromoglycate since, of the studies included in their review, 12 out of 14 conducted before 1981 involved schoolchildren while, of those published since 1981, nine out of 10 involved preschoolchildren. The authors point out that “age of the children . . . was strongly correlated with year of publication”. They chose to interpret the positive eVect size of older studies as an indication of publication bias. An equally reasonable interpretation might be that sodium cromoglycate is more eVective in schoolchildren than in preschoolchildren. I wonder if the authors could calculate the size of the treatment eVect in their selected trials separately for those trials predominantly involving schoolchildren and those involving predominantly pre-schoolchildren. Systematic review and meta-analysis often lend spurious objectivity to the assessment of eYcacy. In the final event statistics provide guidance, and some form of subjective judgement is required as to the clinical relevance of the analysis.