Quantifying, displaying and accounting for heterogeneity in the meta-analysis of RCTs using standard and generalised Q statistics

Jack Bowden, Jayne F Tierney, Andrew J Copas, Sarah Burdett

Research output: Contribution to journalArticle (Academic Journal)peer-review

380 Citations (Scopus)


BACKGROUND: Clinical researchers have often preferred to use a fixed effects model for the primary interpretation of a meta-analysis. Heterogeneity is usually assessed via the well known Q and I2 statistics, along with the random effects estimate they imply. In recent years, alternative methods for quantifying heterogeneity have been proposed, that are based on a 'generalised' Q statistic.

METHODS: We review 18 IPD meta-analyses of RCTs into treatments for cancer, in order to quantify the amount of heterogeneity present and also to discuss practical methods for explaining heterogeneity.

RESULTS: Differing results were obtained when the standard Q and I2 statistics were used to test for the presence of heterogeneity. The two meta-analyses with the largest amount of heterogeneity were investigated further, and on inspection the straightforward application of a random effects model was not deemed appropriate. Compared to the standard Q statistic, the generalised Q statistic provided a more accurate platform for estimating the amount of heterogeneity in the 18 meta-analyses.

CONCLUSIONS: Explaining heterogeneity via the pre-specification of trial subgroups, graphical diagnostic tools and sensitivity analyses produced a more desirable outcome than an automatic application of the random effects model. Generalised Q statistic methods for quantifying and adjusting for heterogeneity should be incorporated as standard into statistical software. Software is provided to help achieve this aim.

Original languageEnglish
Pages (from-to)41
JournalBMC Medical Research Methodology
Publication statusPublished - 2011


  • Analysis of Variance
  • Clinical Trials as Topic
  • Data Interpretation, Statistical
  • Humans
  • Meta-Analysis as Topic
  • Neoplasms
  • Randomized Controlled Trials as Topic
  • Statistics as Topic


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