[R-meta] [R=meta] Question about removal of outliers and power calculation

[Cath Kids]

Dear Michael,

Thank you for your reply! Please see more response in blue.

On Tue, Jul 30, 2019 at 6:46 PM Michael Dewey <lists using dewey.myzen.co.uk>
wrote:

> Dear Joanne
>
> In line comments
>
> On 30/07/2019 04:21, Cath Kids wrote:
> > Hello everyone,
> >
> > I am new to meta-analysis and I would like to clarify some conceptual
> > matter:
> >
> > 1. Should I remove outliers before doing subgroup analysis/ meta
> > regression? In my study, heterogeneity became insignificant after removal
> > outliers. I read meta-analyses which did both practice and I wonder which
> > is the correct way.
>
> This raises a number of issues. If heterogeneity exists why do you want
> to reduce or eliminate it? Would it not be better to try to describe and
> explain it? In general removing outliers leads to a model which is data
> dependent rather than the scientific model you started with. The only
> time I would contemplate removing observations would be if there was
> reason to suspect that they are fraudulent, recorded erroneously, did
> not really meet the inclusion criteria after all, or some other
> principled explanation which i cannot think of just now.
>

I see. So I should use all observations for the subgroup analysis/
meta-regression. But then given the heterogeneity of the results, I can
remove the outliers and check whether there is any change in the overall
effect size as a sensitivity analysis. is that right?

>
> > 2. I wonder whether any one of you are familiar with any tools to
> calculate
> > power for meta-analysis of correlation coefficients?
> >
>
> If you are planning a study why do you need power? The number of primary
> studies you find in your literature search is not within your powers to
> choose. You can only analyse what you find, not what you would like to
> find. If you have already done the study then all the required
> information about precision is contained within the confidence estimates
> about your estimate(s).
>
> I refer to this guideline online
https://bookdown.org/MathiasHarrer/Doing_Meta_Analysis_in_R/power-analysis.html
.
However, it does not mention meta-analysis of correlation. So I'm not sure
how to do it.

>
> > Thank you very much!
> >
> > Regards,
> > Joanne
> >
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> --
> Michael
> http://www.dewey.myzen.co.uk/home.html
>

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