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

Luke Martinez m@rt|nez|ukerm @end|ng |rom gm@||@com
Mon Jan 10 13:37:34 CET 2022

Dear Wolfgang,

The studies follow a pre-post-control design. The effect size measure used
is standardized mean difference (SMD).

I hope this clarifies my question.

sudy time  yi
1         0
1         1
2         0
2         1

On Mon, Jan 10, 2022, 5:43 AM Viechtbauer, Wolfgang (SP) <
wolfgang.viechtbauer using maastrichtuniversity.nl> wrote:

> 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

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