[R] dummy encoding in metafor

[Viechtbauer Wolfgang (STAT)]

Dear Alma,

either there is a whole lot of miscommunicaton here, or you (and your supervisor) are way in over your head.

You say that you are working with Cohen's d values. And you mentioned CMA. So, let me ask you some questions:

1) Has CMA computed those d values for you?
2) If yes, what information did you supply to CMA for the computation of those d values? (means, standard deviations, and the sample sizes of the two groups?)
3) Did CMA then provide you with a column of values that are the corresponding sampling variances or standard errors? (those values should NOT all be equal to 1!)

Best,
Wolfgang

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of Alma Wilflinger
> Sent: Sunday, January 27, 2013 21:52
> To: Michael Dewey; r-help at r-project.org
> Subject: Re: [R] dummy encoding in metafor
> 
> Hi Michael!
> 
> Yes, I do use Cohens d. As a matter of fact my thesis supervisor told me
> to use 1 as the value for standard deviation for all of my studies.
> Unfortunately I am not totally sure myself why to do this have you ever
> used such an approach?
> 
> kind regards,
> Alma
> 
> ________________________________
>  From: Michael Dewey <info at aghmed.fsnet.co.uk>
> 
> t.co.uk>; "r-help at r-project.org" <r-help at r-project.org>
> Sent: Thursday, January 24, 2013 6:57 PM
> Subject: Re: [R] dummy encoding in metafor
> 
> At 22:06 23/01/2013, Alma Wilflinger wrote:
> 
> > Hi Michael,
> >
> > The supervisor for my Master's Thesis told me that my means are the
> effect size and cause of this I have to take figure 1 for all standard
> deviations. So I hope that was the right information.
> 
> Alma
> There is a fairly comprehensive list of all the things which might be an
> effect size on
> http://en.wikipedia.org/wiki/Effect_size
> Is what you call Mean one of them?
> 
> 
> >
> > From: Michael Dewey <info at aghmed.fsnet.co.uk>
> 
> wolfgang.viechtbauer at maastrichtuniversity.nl>; Michael Dewey
> <info at aghmed.fsnet.co.uk>; "r-help at r-project.org" <r-help at r-project.org>
> > Sent: Wednesday, January 23, 2013 10:22 AM
> > Subject: Re: [R] dummy encoding in metafor
> >
> > At 08:30 23/01/2013, Alma Wilflinger wrote:
> > > Dear Wolfgang and Michael,
> > >
> [[elided Yahoo spam]]
> > >
> > > Concerning the Variance: I took the variance I used for CMA (which
> is always 1), so I think it should be the right one.
> >
> > It seems unlikely to me that the variance from each study would be the
> same although I suppose it could be possible. Are you sure you are
> supplying the right values to CMA?
> >
> >
> > > Thank you for noticing and mentioning though :)
> > >
> > > I really appreciate how helpful you both are.
> > >
> > > best,
> > > Alma