[R-meta] Problem with sigma-square in 3-level meta-analysis
@eb@@t|@n@roeh| @end|ng |rom un|-tueb|ngen@de
Fri Mar 10 08:40:00 CET 2023
We are conducting meta-analyses of correlational effects which are clustered in studies (or independent samples). Therefore we are using 3-level hierarchical random effects models (Sampling error within effect sizes within independent samples).
For one of our sub-analyses which 50 effects of 8 independent samples, the results of the rma.mv pointed to nearly no (5.710374e-12) variance component between the samples:
> overall_mod_cc <- rma.mv(zr, V=var, random = ~ 1| Sample_ID / nummer, data = data_cc, method = "REML")
Multivariate Meta-Analysis Model (k = 50; method: REML)
estim sqrt nlvls fixed factor
sigma^2.1 0.0000 0.0000 8 no Sample_ID
sigma^2.2 0.0222 0.1489 50 no Sample_ID/nummer
However, when I look directly at the manifest variances for the group means (0.225) and all effects (0.392), I conclude that there should actually be a much larger variance component between the independent samples.
(a) Am I making a thinking error here?
(b) Or could this be because the estimation of variance components using rma.mv() does not work reliably for the small number of studies (8)?
(c) And if (b) is correct - what model or function could I use instead for this partial analysis?
Thanks a lot for your help!
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