[R-meta] moderator and adjusted effects

[Michael Dewey]

Dear Valeria

Comments in-line

On 14/12/2020 17:13, Valeria Ivaniushina wrote:
> Dear experts,
> 
> In my sample of articles for meta-analysis there are three categories, or
> three conditions, that may influence the effect of interest.
> 
> I am more interested in estimating different effects from these conditions
> than in explaining heterogeneity in effect sizes.
> 1) I can do a meta-analysis for each of these conditions separately and get
> three different mean effect sizes.
> 2) Or I can do a meta-analysis of the whole sample, then include a
> condition as a moderator and calculate adjusted effects as described here :
> http://www.metafor-project.org/doku.php/tips:computing_adjusted_effects
> 
I would go for option two as it will give you estimates of the 
differences between the levels of your moderator.

> Which option is better?
> 
> Additional question:  when I include a categorical moderator, is it the
> same as including a dummy variable in a regression?
> How can I specify that the variable is categorical with 3 levels?
>

If you make the moderator a factor then R will take care of this for you.

> Best,
> Valeria
> 
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> 
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-- 
Michael
http://www.dewey.myzen.co.uk/home.html