While you may get a helpful reply, I think this is really not the forum for such relatively basic math/stat questions. As you seem to be more or less at sea here, I really really suggest that you seek help from a local statistical resource.
Cheers, Bert Bert Gunter Genentech Nonclinical Biostatistics (650) 467-7374 "Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." Clifford Stoll On Sun, Dec 7, 2014 at 10:25 PM, Purssell, Ed <ed.purss...@kcl.ac.uk> wrote: > Dear All > > I have tried very hard to work out what to do with putting logged data into > metafor; the paper says.. > 'geometric mean antibody concentrations (GMCs) or opsonophagocytic activity > titres (geometric mean titres [GMT]) were calculated with 95% CIs by taking > the antilog of the mean of the log concentration or titre transformations.' > > Does this look right if I take the reported mean, upper and lower bound of > the CI, and the number? > > m<-log(mean) > ub<-log(upper bound) > lb<-log(lower bound) > diff<-ub-lb > SE<-diff/3.92 > SD<-SE*(sqrt(n)) > > Then put m, SD and n for each group into metafor as normal. Or is there a > better way? I am afraid I didn't understand how to do it on a log scale. > > Thank you > > Edward > ---------------------------- > Edward Purssell PhD > Senior Lecturer > > Florence Nightingale Faculty of Nursing and Midwifery > King's College London > James Clerk Maxwell Building > 57 Waterloo Road > London SE1 8WA > Telephone 020 7848 3021 > Mobile 07782 374217 > email edward.purss...@kcl.ac.uk > https://www.researchgate.net/profile/Edward_Purssell > > ________________________________________ > From: Viechtbauer Wolfgang (STAT) > <wolfgang.viechtba...@maastrichtuniversity.nl> > Sent: 14 November 2014 10:40 > To: Michael Dewey; Purssell, Ed; r-help@r-project.org > Subject: RE: [R] metafor - code for analysing geometric means > > With "geometric mean 1 CI /3.92", I assume you mean "(upper bound - lower > bound) / 3.92". Two things: > > 1) That will give you the SE of the mean, not the SD of the observations > (which is what you need as input). > > 2) Probably the CI for the geometric mean was calculated on the log-scale (as > Michael hinted at). Check if log(upper bound) and log(lower bound) is (within > rounding error) symmetric around log(geometric mean). Then (log(upper bound) > - log(lower bound)) / 3.96 * sqrt(n) will give you the SD of the log of the > values used to compute the geometric mean. Then you could use log(geometric > mean) and that SD as input. But this would give you the difference of the > log-transformed geometric means. Not sure if this is what you want to analyze. > > Two more articles that may be helpful here: > > Friedrich, J. O., Adhikari, N. K., & Beyene, J. (2012). Ratio of geometric > means to analyze continuous outcomes in meta-analysis: Comparison to mean > differences and ratio of arithmetic means using empiric data and simulation. > Statistics in Medicine, 31(17), 1857-1886. > > Souverein, O. W., Dullemeijer, C., van 't Veer, P., & van der Voet, H. > (2012). Transformations of summary statistics as input in meta-analysis for > linear dose-response models on a logarithmic scale: A methodology developed > within EURRECA. BMC Medical Research Methodology, 12(57). > > Best, > Wolfgang > >> -----Original Message----- >> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] >> On Behalf Of Michael Dewey >> Sent: Thursday, November 13, 2014 12:36 >> To: Purssell, Ed; r-help@r-project.org >> Subject: Re: [R] metafor - code for analysing geometric means >> >> On 13/11/2014 11:00, Purssell, Ed wrote: >> > ?Dear All >> > >> > I have some data expressed in geometric means and 95% confidence >> intervals. Can I code them in metafor as: >> > >> > rma(m1i=geometric mean 1, m2i=geometric mean 2, sd1i=geometric mean 1 >> CI /3.92, sd2i=geometric mean 2 CI/3.92.......etc, measure="MD") >> >> Would it not be better to work on the log scale? >> >> > All of the studies use geometric means. >> > >> > Thanks! >> > >> > Edward >> >> -- >> Michael >> http://www.dewey.myzen.co.uk > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
