[R-meta] meta-regression: categorical

[P. Roberto Bakker]

Hi Wolfgang,

Thank you for your information and explanation.

Bw Roberto

2018-04-24 12:25 GMT+02:00 Viechtbauer, Wolfgang (SP) <
wolfgang.viechtbauer at maastrichtuniversity.nl>:

> Hi Roberto,
>
> If you put a character variable (or a factor) into a formula, it is
> automatically dummy coded. Actually, the type of coding depends on:
>
> options("contrasts")
>
> But the default for that is:
>
>         unordered           ordered
> "contr.treatment"      "contr.poly"
>
> And help(contr.treatment) explains what kind of coding this is, namely the
> 'usual' dummy coding where one level is the 'reference' level (and whose
> dummy gets omitted).
>
> Best,
> Wolfgang
>
> -----Original Message-----
> From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-
> bounces at r-project.org] On Behalf Of P. Roberto Bakker
> Sent: Tuesday, 24 April, 2018 11:14
> To: r-sig-meta-analysis at r-project.org
> Subject: [R-meta] meta-regression: categorical
>
> Hi everybody,
>
> In:
> http://www.metafor-project.org/doku.php/analyses:vanhouwelingen2002
> 'allocation' is put in syntax without dummy coding
>
> rma <http://finzi.psych.upenn.edu/library/metafor/html/rma.uni.html>(yi,
> vi, mods = ~ alloc, data
> <http://stat.ethz.ch/R-manual/R-devel/library/utils/html/data.html>=dat,
> method="ML")
>
> If I am not wrong, 'allocation' is a catergorical variabel, and I suppose
> the R handles the coding of dummy automatically.
> Correct?
>
> I found this information in:
> https://cran.r-project.org/web/packages/metafor/metafor.pdf
> *Categorical moderator variables can be included in the model via the mods
> argument in the same way that appropriately (dummy) coded categorical
> independent variables can be included in linear models. One can either do
> the dummy coding manually or use a model formula together with the factor
> function to let R handle the coding automatically.   *
>
> *Best wishes and thank you in advance*
> *Roberto*
>

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