Without the sample size of a study (i.e., either the group sizes or the total sample size), you cannot convert the p-value to a t-value or a t-value to a d-value. And for studies where you have the d-value but no sample size, you cannot compute the corresponding sampling variance. So, without additional information, you cannot include these studies. Maybe studies where a d-value is directly reported also report a CI for the d-value? Then the sampling variance can be back-calculated (since a 95% CI for d is typically computed with d +- 1.96 sqrt(vi), where vi is the sampling variance).
Best, Wolfgang > -----Original Message----- > From: Verena Weinbir [mailto:vwein...@gmail.com] > Sent: Tuesday, May 06, 2014 15:09 > To: Michael Dewey > Cc: Viechtbauer Wolfgang (STAT); r-help@r-project.org > Subject: Re: [R] Metafor: How to integrate effectsizes? > > Thank you very much for your illustration, Wolfgang! It helped me a > lot. And also thank you for the package-hint, Michael! > > Now, I have re-checked the respective studies, and there still are a > couple of studies left, only stating cohens d, and the respective t-value > and p-value - sample and group sizes are not addressed (its data from an > older meta-analysis). Is there a way to embed these studies in my sample? > Wolfgangs illustration addresses only cases in which group sizes are > stated, if I understand you correctly... > > Many thanks in advance, > > Verena > > On Sat, Apr 26, 2014 at 1:38 PM, Michael Dewey <i...@aghmed.fsnet.co.uk> > wrote: > At 20:34 25/04/2014, Viechtbauer Wolfgang (STAT) wrote: > 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: > > http://www.metafor-project.org/doku.php/tips:assembling_data_smd > > Verena might also like to look at the compute.es package available from > CRAN to see whether any of the conversions programmed there do the job. > > > Best, > Wolfgang > > -- > 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-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] > > On Behalf Of Michael Dewey > > Sent: Friday, April 25, 2014 16:23 > > To: Verena Weinbir > > Cc: r-help@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:i...@aghmed.fsnet.co.uk>i...@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 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
