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This article describes an updated version of the metabias command, which provides statistical tests for funnel plot asymmetry. In addition to the previously implemented tests, metabias implements two new tests that are recommended in the recently updated Cochrane Handbook for Systematic Reviews of Interventions (Higgins and Green 2008). The first new test, proposed by Harbord, Egger, and Sterne (2006, Statistics in Medicine 25: 3443–3457), is a modified version of the commonly used test proposed by Egger et al. (1997, British Medical Journal 315: 629–634). It regresses Z/√V against √V, where Z is the efficient score and V is Fisher’s information (the variance of Z under the null hypothesis). The second new test is Peters’ test, which is based on a weighted linear regression of the intervention effect estimate on the reciprocal of the sample size. Both of these tests maintain better control of the false-positive rate than the test proposed by Egger at al., while retaining similar power.

Meta-analysis of diagnostic test accuracy presents many challenges. Even in the simplest case, when the data are summarized by a 2 × 2 table from each study, a statistically rigorous analysis requires hierarchical (multilevel) models that respect the binomial data structure, such as hierarchical logistic regression. We present a Stata package, metandi, to facilitate the fitting of such models in Stata. The commands display the results in two alternative parameterizations and produce a customizable plot. metandi requires either Stata 10 or above (which has the new command xtmelogit), or Stata 8.2 or above with gllamm installed.

This article describes updates of the meta-analysis command metan and options that have been added since the command’s original publication (Bradburn, Deeks, and Altman, metan — an alternative meta-analysis command, Stata Technical Bulletin Reprints, vol. 8, pp. 86–100). These include version 9 graphics with flexible display options, the ability to meta-analyze precalculated effect estimates, and the ability to analyze subgroups by using the by() option. Changes to the output, saved variables, and saved results are also described.

We present a revised version of the metareg command, which performs meta-analysis regression (meta-regression) on study-level summary data. The major revisions involve improvements to the estimation methods and the addition of an option to use a permutation test to estimate p-values, including an adjustment for multiple testing. We have also made additions to the output, added an option to produce a graph, and included support for the predict command. Stata 8.0 or above is required.

Funnel plots are a visual tool for investigating publication and other bias in meta-analysis. They are simple scatterplots of the treatment effects estimated from individual studies (horizontal axis) against a measure of study size (vertical axis). The name “funnel plot” is based on the precision in the estimation of the underlying treatment effect increasing as the sample size of component studies increases. Therefore, in the absence of bias, results from small studies will scatter widely at the bottom of the graph, with the spread narrowing among larger studies. Publication bias (the association of publication probability with the statistical significance of study results) may lead to asymmetrical funnel plots. It is, however, important to realize that publication bias is only one of a number of possible causes of funnel-plot asymmetry—funnel plots should be seen as a generic means of examining small study effects (the tendency for the smaller studies in a meta-analysis to show larger treatment effects) rather than a tool to diagnose specific types of bias. This article introduces the metafunnel command, which produces funnel plots in Stata. In accordance with published recommendations, standard error is used as the measure of study size. Treatment effects expressed as ratio measures (for example risk ratios or odds ratios) may be plotted on a log scale.