At 09:42 30/03/2014, Purssell, Ed wrote:
Dear All
I have a question about combining effect sizes generated by escalc
in metafor. I realise these may be stupid things to do; but they
are deliberately so to explain what I mean - I don't intend doing this!
I have 3 studies; each of which has a different measure of
effect/presents the data differently, so I use escalc to calculate
the effect size of each and combine them into a data-frame:
es1<-escalc(measure="MD", m1i=10 , m2i=5 , n1i=12 , n2i=12, sd1i=2, sd2i=2)
es2<-escalc(measure="RR", ai=10 , bi=5 , ci=12 , di=12)
es3<-escalc(measure="RR", ai=10 , ci=5 , n1i=15 , n2i=12)
es4<-rbind(es1, es2, es3) # combines the 3 effect sizes into a data frame
attach(es4) # makes the data frame available to R
Not that it is relevant here but it is better not to do that. Just
use the data = parameter
es5<-rma(yi, vi, data=es4) # running the meta analysis here gives
the error message
Error in rma(yi, vi, data = es4) :
Length of yi and ni vectors are not the same.
There is some glitch here which is setting the "ni" attribute of yi
inappropriately
Try going
attr(es4$yi, "ni") <- NULL
ad then call rma.uni again
But if I save this as a .csv and open it in R using
read.csv("E:/es5.csv", etc) i get a data frame that looks like this:
yi vi
1 5.0000 0.6667
2 0.6931 0.4667
3 0.4700 0.1500
I can run it using
rma(yi, vi, data=es4)
I have three questions.
1. Can escalc be used in this way to calculate each study effect
size indvidually and then rbinding them into a data-frame (assuming
that it is a sensible thing to do, which I realise the above probably isn't)?
2. What is the meaning of the error message:
Error in rma(yi, vi, data = es4) :
Length of yi and ni vectors are not the same.
3. Is it right to save it as a .csv, open it and re-run it as I have done?
That gets rid of the attributes.
Thanks very much, and to Wolfgang thanks for a great programme! I am
using it in my MSc teaching here for healthcare students.
Edward
[[alternative HTML version deleted]]
Michael Dewey
i...@aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html
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