[R-meta] Moderator Analysis

Michael Dewey ||@t@ @end|ng |rom dewey@myzen@co@uk
Wed Feb 10 12:17:22 CET 2021


Dear Jake

Untested, but I wonder if using mod = ~ f.c - 1 would give you what you 
desire.

Michael

On 10/02/2021 04:37, Jake Downs wrote:
> Hello R Friends,
> I am a doc student newish to R  and meta-analysis. It's a lot to wrap my
> brain around, but I'm eager to learn.
> 
> I am conducting a 3-level meta-analysis using rma.mv on student reading
> outcomes for various types of related practices. Level one is effect sizes,
> level two models covariance between effect sizes within studies, and level
> three models covariance between studies.
> 
> The meta-analysis is multivariate, so level one outcomes are coded as
> either "fluency" or "comprehension."  I have ran the analysis for all
> effects (g=0.58; code below), but I am also very interested in producing a
> 'fluency' effect size and a 'comprehension' effect size. I would like
> assistance to figure out the best way to do that.
> 3 Level Fit:
> rq1.fit1 <- tx.cg %>%
>    rma.mv(
>      yi = tx.cg.yi,  #fit one, 3 level meta-analysis
>      V = tx.cg.vi,
>      random = ~ 1 | study.number/effect.number,
>      level=95,
>      digits=2,
>      data = .,
>      method = "REML"
>    )
> summary(rq1.fit1)
> 
> Option 1:
> Moderator analysis. I ran a moderator analysis using this code:
> rq2.f.c <- tx.cg %>%
>    metafor::rma.mv(
>      yi = tx.cg.yi,
>      V = tx.cg.vi,
>      random = ~ 1 | study.number/effect.number,
>      level=95,
>      digits=2,
>      data = .,
>      method = "REML",
>      mods = ~ f.c)
> summary(rq2.f.c)
> 
> The QM test of moderators is approaching statistical significance (p =
> 0.08), however the intercept (reference group of comprehension) did report
> statistically significant results. Does that mean that only comprehension
> moderates outcomes? (And that only a comprehension 'effect size' would be
> valid?)
> 
> Option 2: Single Variable Moderator analysis?
> To calculate an effect size for fluency and comprehension, is there a way
> to run a single variable as a moderator? For example, rather than running
> fluency and comprehension in a combined moderator analysis run
> comprehension only in one moderator analysis and fluency only in another?
> Is this a viable method?
> 
> Option 3: Subset Independent Meta-analysis
> I don't think this option is viable, but I could use the subset = function
> in metafor to run an analysis using ONLY comprehension, and using ONLY
> fluency. This would throw away half my data however, which I think would
> limit the validity of my findings.
> 
> In short: I just want to be able to say that the effect size for fluency
> was X and the effect size for comprehension was Y. What is the best way to
> do that?
> 
> 
> Thanks very much for your help.
> 
> Jake
> 
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> 
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-- 
Michael
http://www.dewey.myzen.co.uk/home.html



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