[R-meta] Estimating "overall effect" in meta-regression

[Viechtbauer, Wolfgang (SP)]

Dear Luke,

I don't understand the question, in part because it is not clear to me what kind of design the studies have and what kind of effect size measure you are using. Could you clarify this?

Best,
Wolfgang

>-----Original Message-----
>From: Luke Martinez [mailto:martinezlukerm using gmail.com]
>Sent: Sunday, 09 January, 2022 7:53
>To: R meta
>Cc: Viechtbauer, Wolfgang (SP)
>Subject: Estimating "overall effect" in meta-regression
>
>Dear R-meta Community,
>
>I'm meta-analyzing a group of pre-post studies. My first RQ is: what
>is the "overall effect" of policy X on a dependent variable.
>
>I know that I can fit an intercept-only model to answer this RQ.
>
>But an intercept-only model estimates the average effect size across
>BOTH pre-tests (before policy X implementation) and post-tests (after
>policy X implementation), while pre-test effect sizes don't contain
>any policy X effect.
>
>Given that, is it appropriate to use an intercept-only model to answer
>this RQ, or I actually need to use a time indicator as a moderator to
>separate the pre- from post-test effect sizes to answer this RQ (in
>which case the original RQ must change too)?
>
>Thank you for helping me better conceptualize this basic question,
>Luke