[R-meta] rma.mv: why some var components change but others don't across 2 models

[Stefanou Revesz]

Dear Wolfgang and Expert List Members,

Why `study` with 57 levels in model `res` gives `sigma^2.1 = 0.0200`
but `study` with 57 levels in model `res2` gives `sigma^2.1  =
0.0122`?
(SAME LEVELS BUT DIFFERENT RESULTS)

Why `outcome` with 4 levels in model `res` gives `sigma^2.2 = 0.0093`
but `outcome` with 68 levels in model `res2` gives `sigma^2.2  =
0.0093`?
(DIFFERENT LEVELS BUT SAME RESULTS)

For reproducibility, below are my data and code.

Many thanks to you all,
Stefanou

m <- read.csv("https://raw.githubusercontent.com/fpqq/w/main/c.csv")

res <- rma.mv(yi, vi, random = list(~ 1 | study, ~1|outcome, ~ 1 |
measure), data=m)
                    estim       sqrt  nlvls  fixed   factor
sigma^2.1  0.0200  0.1415     57     no    study
sigma^2.2  0.0093  0.0964      4     no  outcome
sigma^2.3  0.0506  0.2249      7     no  measure

res2 <- rma.mv(yi, vi, random = list(~ 1 | study/outcome, ~ 1 |
measure), data=m)
                    estim       sqrt  nlvls  fixed         factor
sigma^2.1  0.0122  0.1105     57     no          study
sigma^2.2  0.0093  0.0964     68     no  study/outcome
sigma^2.3  0.0363  0.1904      7     no        measure