[R-meta] R-sig-meta-analysis Digest, Vol 35, Issue 7
Hi Wolfgang, Let me start by just using the example on Metafor help. I used the dataset provided in the example on the Metafor page: http://www.metafor-project.org/doku.php/tips:bootstrapping_with_ma. I was able to replicate the results on the page. Then I added the variable alloc as a moderator variable in the estimation. ##Code #Bootstrapping res <-rma.mv(yi, vi, random = ~ 1 | trial, data=dat, mods = ~ alloc) boot.func <- function(df, indices) { sub <- dat[indices,] res <-rma.mv(yi, vi, random = ~ 1 | trial, data=dat, mods = ~ alloc) if (is.element("try-error", class(res))) NA else c(coef(res), vcov(res)) } library(boot) set.seed(8781328) res.boot <- boot(dat, boot.func, R=10000) boot.ci(res.boot, index=1:2) #CI for average effect boot.ci(res.boot, index=3:4) #CI for tau2 ## Output Bootstrap Statistics : original bias std. error t1* -0.51792376 0 0 t2* -0.44786464 0 0 t3* 0.08899601 0 0 t4* 0.19465035 0 0 t5* -0.19465035 0 0 t6* -0.19465035 0 0 t7* -0.19465035 0 0 t8* 0.26607085 0 0 t9* 0.19465035 0 0 t10* -0.19465035 0 0 t11* 0.19465035 0 0 t12* 0.31363498 0 0 Error in sort.int(x, na.last = na.last, decreasing = decreasing, ...) : index 0 outside bounds In addition: Warning messages: 1: In sqrt(tv[, 2L]) : NaNs produced 2: In norm.inter(z, (1 + c(conf, -conf))/2) : extreme order statistics used as endpoints Best Tarun Tarun Khanna PhD Researcher Hertie School Friedrichstra?e 180 10117 Berlin ? Germany khanna at hertie-school.org ? www.hertie-school.org<http://www.hertie-school.org/>
From: Viechtbauer, Wolfgang (SP) <wolfgang.viechtbauer at maastrichtuniversity.nl>
Sent: 21 April 2020 15:05:08
To: Tarun Khanna; r-sig-meta-analysis at r-project.org
Subject: RE: R-sig-meta-analysis Digest, Vol 35, Issue 7
Sent: 21 April 2020 15:05:08
To: Tarun Khanna; r-sig-meta-analysis at r-project.org
Subject: RE: R-sig-meta-analysis Digest, Vol 35, Issue 7
Yes, one can also use bootstrapping on regression coefficients. Please provide a fully reproducible example that illustrates your attempts. Best, Wolfgang >-----Original Message----- >From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-project.org] >On Behalf Of Tarun Khanna >Sent: Tuesday, 21 April, 2020 14:35 >To: r-sig-meta-analysis at r-project.org >Subject: Re: [R-meta] R-sig-meta-analysis Digest, Vol 35, Issue 7 > >Dear Wolfgang, > >I have a follow up question to Crystals'. Does bootstrapping also work with >regressions that have moderator variables? > >I used the link that you provided, http://www.metafor- >project.org/doku.php/tips:bootstrapping_with_ma, and ran a regression with >"alloc" as a moderator variable and then tried bootstrapping the errors but >the std. errrs were calculated as zero. This is the output that i got: > >Bootstrap Statistics : > original bias std. error >t1* -0.51792376 0 0 >t2* -0.44786464 0 0 >t3* 0.08899601 0 0 >t4* 0.19465035 0 0 >t5* -0.19465035 0 0 >t6* -0.19465035 0 0 >t7* -0.19465035 0 0 >t8* 0.26607085 0 0 >t9* 0.19465035 0 0 >t10* -0.19465035 0 0 >t11* 0.19465035 0 0 >t12* 0.31363498 0 0 > >> boot.ci(res.boot, index=1:2) #CI for average effect >Error in sort.int(x, na.last = na.last, decreasing = decreasing, ...) : > index 0 outside bounds >In addition: Warning messages: >1: In sqrt(tv[, 2L]) : NaNs produced >2: In norm.inter(z, (1 + c(conf, -conf))/2) : > extreme order statistics used as endpoints > >I also tried doing it with my own data set and got the following error: > >Error in t.star[r, ] <- res[[r]] : > number of items to replace is not a multiple of replacement length >In addition: There were 50 or more warnings (use warnings() to see the first >50) > >If bootstrapping does indeed work with moderator variables, what might be >wrong? > >Best >Tarun > >Tarun Khanna >PhD Researcher >Hertie School > >Friedrichstra?e 180 >10117 Berlin ? Germany >khanna at hertie-school.org ? www.hertie-school.org<http://www.hertie-<http://www.hertie-school.org<http://www.hertie-> >school.org/>