[R-meta] Studies with more than one control group

Jack Solomon kj@j@o|omon @end|ng |rom gm@||@com
Wed Jun 23 20:35:55 CEST 2021

Hello All,

I have come across a couple of primary studies in my meta-analytic pool
that have used two comparison/control groups (as the definition of
'control' has been debated in the literature I'm meta-analyzing).

(1) Given that, should I create an additional column ('control') to
distinguish between effect sizes (SMDs in this case) that have been
obtained by comparing the treated groups to control 1 vs. control 2 (see

(2) If yes, then, does the addition of a 'control' column call for the
addition of a random effect for 'control' of the form:  "~ |
studyID/controlID" (to be empirically tested)?

(3) If I later decide to drop controlID from my dataset, I think I can
still keep all effect sizes from both control groups intact without any
changes to my coding scheme, right?

Thanks, Jack

***consider 'control' in coding:
studyID  yi  controlID
1             .1      1
1             .2      2
1             .3      1
1             .4      2
2             .5      1
2             .6      2
3             .7      1

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