[R-meta] Subgroup analyses

[Philippe Tadger]

Dear David

You can see answer to your question here:

https://www.metafor-project.org/doku.php/tips:models_with_or_without_intercept 
<https://www.metafor-project.org/doku.php/tips:models_with_or_without_intercept>

https://stats.stackexchange.com/questions/191144/interpreting-intercept-only-meta-analysis-model-when-effect-size-is-raw-mean 
<https://stats.stackexchange.com/questions/191144/interpreting-intercept-only-meta-analysis-model-when-effect-size-is-raw-mean>

https://stat.ethz.ch/pipermail/r-sig-meta-analysis/2018-May/000818.html 
<https://stat.ethz.ch/pipermail/r-sig-meta-analysis/2018-May/000818.html>

I would not substract the intercept, in most of the cases is a strong 
assumption.

On 25/08/2021 12:55, David Cicchetti wrote:
>
> Dear list members,
>
> I am trying to run subgroup analyses in my meta analysis. I have the 
> issue that I do not know whether I should include an intercept or not, 
> meaning whether I should do mods = ~ Coil.Type (with intercept) or 
> mods = ~ Coil.Type - 1 (without intercept).
>
> From what I know so far we can leave out the intercept if for x = 0 -> 
> y = 0. Unfortunately I don't think that logic applies here. My 
> variables (as for example Coil Type) do not have a 'zero' condition, 
> it compares for example Coil A with Coil B.
> If I want to write down the values as a table, I cannot do that well 
> when including the intercept because then the estimate, standard error 
> and CI are from the difference to the intercept and not from the level 
> itself.
>
> Since the Moderator tests become more easily significant when 
> excluding the intercept, I was hesitant to do so. Therefore I would be 
> thankful if anyone could clear me up on when/if I am allowed to get 
> rid of the Intercept in my case.
>
> Thanks in advance.
>
> Best,
> David
>
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-- 
Kind regards/Saludos cordiales
*Philippe Tadger*
ORCID <https://orcid.org/0000-0002-1453-4105>, Reseach Gate 
<https://www.researchgate.net/profile/Philippe-Tadger>
Phone/WhatsApp: +32498774742

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