# [R-meta] Help with meta-analisys of variation

Viechtbauer, Wolfgang (SP) wo||g@ng@v|echtb@uer @end|ng |rom m@@@tr|chtun|ver@|ty@n|
Thu Jul 18 12:25:43 CEST 2019

```Dear Fernando,

I am not sure I fully understand your question. My interpretation of your question/problem is as follows. You have studies that measure some property of interest in a group of a subjects at multiple timepoints. And for each timepoint, you compute ln(SD) with sampling variance 1/(2*(n-1)). But since multiple ln(SD) values are based on the same sample of subjects, you want to compute the covariance between those ln(SD) values and you are not sure how to do that. Is this the essence of your question?

Best,
Wolfgang

-----Original Message-----
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces using r-project.org] On Behalf Of Fernando Klitzke Borszcz
Sent: Thursday, 11 July, 2019 15:42
To: r-sig-meta-analysis using r-project.org
Subject: [R-meta] Help with meta-analisys of variation

Hi all,

I am conducting a meta-analysis about standard deviations of change between
2 conditions in the metafor package. I am using effect sizes (lnSD) and
their sampling variance, based on Nakagawa et al. (
https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.12309).
However, many studies included in my analysis, the same subject produces
multiple results (multiple time points). Thus, I should determine the
variance-covariance matrix of the effects. However, I am not sure if it is
appropriate to determine the variance-covariance matrix using any
correlation value for this type of effect, because effects variances are
based only on the sample size (1/2[n-1]). Is there any alternative to
determine the variance-covariance matrix for this type of data, or I should
just include the study as a random effect?

Best wishes!

Att.
Fernando Borszcz
```