Comparing and combining studies of bronchial responsiveness.

BACKGROUND There is no standardised protocol for the measurement of bronchial responsiveness. Results from different studies are difficult to compare and combine. METHODS Analyses are divided between those of a continuous outcome, which can be directly standardised as effect size, and those based on a binary outcome. A published method is used to convert an odds ratio to equivalent effect size. RESULTS The use of effect size allows comparison between studies using a continuous outcome but different protocols, provided the relevant standard deviation is reported. Effect size from a continuous outcome and that derived from an odds ratio from an equivalent analysis gave similar results. CONCLUSIONS Systematic reviews which include both continuous effect estimates and odds ratios can include both in one meta-analysis, provided relevant standard deviations are published for the former. Authors are encouraged to report these in all fields in which measurement protocols vary.