Meta-analysis in Stata: history, progress and prospects

Systematic reviews of randomised trials are now widely recognised to be the best way to summarise the evidence on the effects of medical interventions. A systematic review may (though it need not) contain a meta-analysis, `a statistical analysis which combines the results of several independent studies considered by the analyst to be "combinable" '. The first researcher to do a meta-analysis was probably Karl Pearson, in 1904. Sadly, Stata was not available at this time. The first Stata command for meta-analysis - the meta command - was published in the Stata Technical Bulletin in 1997, and exploited a facility, introduced in Stata version 5, to program graphics. It requires the user to derive an estimate of the effect of intervention, together with its standard error, for each study. The metan command, published in 1998, does analyses based on the 2 x 2 table for each study, and provides more detailed graphical displays. Facilities for cumulative meta-analysis and meta-regression, and tools for examining bias in meta-analysis, have since been introduced. It is perhaps surprising that Stata commands for meta-analysis are still entirely user-written. This means that the existing commands that produce graphics (a major advantage of the Stata commands compared with those available in other statistical packages) are outdated since the introduction of Stata 8 graphics. Possible ways forward will be discussed, and the talk will conclude with a discussion of developments in meta-analysis that could usefully be addressed by future Stata commands.