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When using meta-regression with factor moderators, result differ a bit from using seperate estimation based on subgroup, even if the same model (mixed effects) is used for both. I understand the difference mostly stems from estimation of $\tau^2$. I can't say from data, but it seem the subgroup-based method is more usually used for forest plots.

I'm using R and metafor, and it's easy to add subgroup polygons, but not with results from meta-regression. Am I wrong in assuming this is for a reason? Wouldn't it be better to display results from meta-regresson, unlessof course differences in amount of heterogeneity are of interest?

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The difference between subgrouping versus using a meta-regression model is explained in detail here:

http://www.metafor-project.org/doku.php/tips:comp_two_independent_estimates

Indeed, it comes down to estimating a single $\tau^2$ value in the meta-regression model versus different $\tau^2$ values when using subgrouping. But one can also fit the meta-regresssion model with different $\tau^2$ values for each level of the factor, in which case the two approaches are identical.

I don't know why you find it difficult to add polygons based on predicted effects to a forest plot. An example of that is provided under help(addpoly.default) (yes, the examples given there is based on a continuous moderator, but the same principle is easily adapted when the moderator is a factor).

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  • $\begingroup$ Thanks @Wolfgang, both fir the answer and the wonderful package. $\endgroup$ – Ozeuss May 2 '16 at 5:16

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