Measuring inconsistency in meta-analyses

Abstract

Cochrane Reviews have recently started including the quantity I2 to help readers assess the consistency of the results of studies in meta-analyses. What does this new quantity mean, and why is assessment of heterogeneity so important to clinical practice?

Figures

Fig 1

Eight trials of amantadine for prevention of influenza. Outcome is cases of influenza. Summary odds ratios calculated with random effects method

Fig 2

Distribution of observed values of I2 based on odds ratios from 509 meta-analyses of dichotomous outcomes in the Cochrane Database of Systematic Reviews. Data are from the first subgroup (if any) in the first meta-analysis (if any) in each review, if it involved a dichotomous outcome and at least two trials with events. Meta-analyses conducted with metan in STATA

Fig 3

Meta-analyses of six case-control studies relating residential exposure to electromagnetic fields to childhood leukaemia. Summary odds ratio calculated by random effects method