[R-meta] To include or not include time in rma.mv

[Yuhang Hu]

Hello All,

I'm considering two candidate fixed-effects structures (cat_mod
= categorical moderator) to meta-analyze a group of longitudinal
studies (pre-test and follow-ups):

m1 = rma.mv(yi ~ 0 + cat_mod + covariates, random = ~ 1 | study/effect)
m2 = rma.mv(yi ~ 0 + cat_mod*time + covariates, random = ~ 1 | study/effect)

In several authoritative meta-analyses of longitudinal studies such as
***https://doi.org/10.1080/19345747.2021.2009072*** and
***https://doi.org/10.1007/s11121-021-01246-3***, I noticed the authors
used "m1" over "m2".

But I was wondering, wouldn't, ignoring "time" (as in "m1") in
the fixed-effects structure mix up the pre-test and follow-up effect
sizes together which can blur our understanding of the treatment effect?

Your guidance is highly appreciated,

Yuhang

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