I've been asked to review the literature for all studies that estimate the mean and median Blood Lead Level (BLL) in a certain country, and then perform a meta-analysis to come up with one overall value for the mean and median level.
Is such a thing typically done? I'm not interested in any "effect size," just a univariate measure.
I'd like to create a forest plot and do some of the standard tests of heterogeneity across studies. Is there a package and function in R that will allow me to do a meta-analysis of mean and median BLLs?
Just to clarify, this would be a separate meta-analysis for means, and a separate meta-analysis for medians.
Best Answer
I thought I would summarize people's suggestions and what I found on my own. It looks like there are meta-analysis methods for analyzing means but not for analyzing medians. These are some sources that are useful for meta-analyzing means:
I was mostly interested in analyzing medians because BLL measurements are almost always highly skewed. However, provided the sample sizes of individual studies are not small, and you are meta-analyzing many studies, the central limit theorem allows you to collapse the individual study means into an overall mean. See the following paper for more explanation: Julian P. T. Higgins et al., Meta-analysis of skewed data: Combining results reported on log-transformed or raw scales, Statist. Med. 2008; 27:6072–6092.