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 adds 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.