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

[Luke Martinez]

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