Dear Chunyan, One possibility would be to use the harmonic mean of the person-time at risk values. You will have to do this manually though at the moment. Here is an example:
### let's just use the treatment group data from dat.warfarin data(dat.warfarin) dat <- escalc(xi=x1i, ti=t1i, measure="IRFT", data=dat.warfarin, append=TRUE) dat ### check if back-transformation of individual IRFT values works transf.iirft(dat$yi, ti=dat$t1i) escalc(xi=x1i, ti=t1i, measure="IR", data=dat.warfarin)$yi ### random-effects models res <- rma(yi, vi, data=dat) res ### harmonic mean of the ti's ti.hm <- 1/(mean(1/dat$t1i)) ### back-transformation using the harmonic mean transf.iirft(res$b, ti=ti.hm) transf.iirft(res$ci.lb, ti=ti.hm) transf.iirft(res$ci.ub, ti=ti.hm) 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 ________________________________________ From: r-help-boun...@r-project.org [r-help-boun...@r-project.org] On Behalf Of Liu, Chunyan [chunyan....@cchmc.org] Sent: Thursday, September 27, 2012 10:48 PM To: r-help@R-project.org Subject: [R] What to use for ti in back-transforming summary statistics from F-T double square-root transformation in 'metafor' Hi Dr. Viechtbauer, I'm doing meta-analysis using your package 'metafor'. I used the 'IRFT' to transform the incident rate. But when I tried to back-transform the summary estimates from function rma, I don't know what's the appropriate ti to feed in function transf.iirft. I searched and found your post about using harmonic mean for ni to back-transform the double arcsine transformation. I'm hoping I can get your help on ti too. Thanks. Chunyan Liu 513-636-9763 Biostatistician II Department of Biostatistics and Epidemiology Cincinnati Children's Hospital Medical Center ______________________________________________ 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.
