[R] Metafor: How to integrate effectsizes?

Viechtbauer Wolfgang (STAT) wolfgang.viechtbauer at maastrichtuniversity.nl
Fri Apr 25 21:34:50 CEST 2014

If you know the d-value and the corresponding group sizes for a study, then it's possible to add that study to the rest of the dataset. Also, if you only know the test statistic from an independent samples t-test (or only the p-value corresponding to that test), it's possible to back-compute what the standardized mean difference is.

I added an illustration of this to the metafor package website:



Wolfgang Viechtbauer, Ph.D., Statistician   
Department of Psychiatry and Psychology   
School for Mental Health and Neuroscience   
Faculty of Health, Medicine, and Life Sciences   
Maastricht University, P.O. Box 616 (VIJV1)   
6200 MD Maastricht, The Netherlands   
+31 (43) 388-4170 | http://www.wvbauer.com   

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of Michael Dewey
> Sent: Friday, April 25, 2014 16:23
> To: Verena Weinbir
> Cc: r-help at r-project.org
> Subject: Re: [R] Metafor: How to integrate effectsizes?
> At 12:33 25/04/2014, you wrote:
> >Thank you very much for your reply and the book recommendation, Michael.
> >
> >Yes, I mean Cohen's d - sorry for the typo :-)
> >
> >Just to make this sure for me: There is no
> >possibility to integrate stated Cohens' ds in an
> >R-Metaanalysis (or a MA at all), if there is no
> >further information traceable regarding SE or the like?
> If there is really no other information like
> sample sizes, significance level, value of some
> significance test then you would have to impute a
> value from somewhere. That would seem a last resort.
> I have cc'ed this back to the list, please keep
> it on the list so others may benefit and contribute.
> >best regards,
> >
> >Verena
> >
> >
> >On Fri, Apr 25, 2014 at 1:21 PM, Michael Dewey
> ><<mailto:info at aghmed.fsnet.co.uk>info at aghmed.fsnet.co.uk> wrote:
> >At 13:15 24/04/2014, Verena Weinbir wrote:
> >Hello!
> >
> >I am using the metafor package for my master's thesis as an R-newbie.
> While
> >calculating effectsizes from my dataset (mean values and
> >standarddeviations) using "escalc" shouldn't be a problem (I hope ;-)),
> I
> >wonder how I could at this point integrate additional studies, which
> only
> >state conhens d (no information about mean value and sds available), to
> >calculate an overall analysis. Â I would be very grateful for your
> support!
> >
> >
> >You mean Cohen's d I think.
> >
> >You will need some more information to enable
> >you to calculate its standard error. Have a look at Rosenthal's chapter
> in
> >@book{cooper94,
> >Â  Â author = {Cooper, H and Hedges, L V},
> >Â  Â title = {A handbook of research synthesis},
> >Â  Â year = {1994},
> >Â  Â publisher = {Russell Sage},
> >Â  Â address = {New York},
> >Â  Â keywords = {meta-analysis}
> >}
> >(There is an updated edition)
> >This gives you more information about converting
> >effect sizes and extracting them from unpromising beginnings.
> >
> >It often requires some ingenuity to get the
> >information you need so have a go and then get
> >back here with more details if you run into problems
> >
> >
> >Best regards,
> >
> >Verena

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