# Calculation for the estimated sampling variance of individual group raw mean

I am conducting a meta-analysis where the effect size is the individual group raw mean (i.e., not raw mean difference). A couple of questions:

1. How (in R: metafor or otherwise) is the estimated sampling variance calculated for these raw means, given sd and n as inputs?

2. If for some of my data points the sd is not reported, can I use some other statistic (I'm not sure what, given there are no group comparisons) to estimate sd so that the estimated sampling variance can be computed?

Well, if you are using metafor and R you can examine the code to see how metafor does it. The sampling variance of a raw mean is $\sigma^2/n$ where $\sigma$ is the standard deviation and $n$ the sample size.