[R-meta] Any limitations in random-effect specification in rma.mv()?

[Timothy MacKenzie]

I have a set of multivariate ('outcome'), longitudinal studies ('time')
that occasionally have used multiple independent samples ('sample') of
subjects and/or more than one control group ('control').   My data
structure looks like:

study outcome time  sample  control obs
1     1       1     1       1       1
1     1       2     2       1       2
1     2       1     1       2       3
1     2       2     2       2       4
2     1       1     1       1       5
2     1       2     1       2       6
3     1       1     1       1       7
3     2       1     2       1       8

I intend to empirically test all possible sources of random variation in
the true effects due to 'study', 'outcome', 'sample', 'control', and
perhaps observations (i.e., each row) differences.

I know I can specify random effects for 'outcome' within studies and 'time'
within study within 'outcome' as follows:

`random = list(~ outcome | study, ~ time | interaction(study,outcome))`

But I was wondering how I could add the random effects for 'sample',
'control', and 'obs'? Ex. Is the following legitimate? Do any of 'control'
or 'sample' need to be crossed effects?

`random = list(~ outcome | study, ~ time | interaction(study,outcome), ~ 1
| sample, ~ 1 | control, ~ 1 | obs)`

Thanks, Tim

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