Hi,

I am a student using R for my final year project, with the metafor package being particularly helpful. I have been following the steps laid out in the manual 'Conducting Meta-analysis in R with the Metafor package' (Viechtbauer, 2010) and applying it to my own data of infected Anopheles mosquitoes across Africa.

In particular, I am attempting to apply a mixed-effect model to my data with absolute latitude as a moderator as per the example in the manual. I am able to generate a plot of Relative Risk against absolute latitude without issue, but when I try to add lines in from the predicted values generated I continually get an error:

Error in xy.coords(x, y) : 'x' and 'y' lengths differ

However, I have used the length function on both my x and y co-ordinates and found no difference in lengths. If anyone could shed some light on this I'd really appreciate it. The code I used can be found below:

> mixed<-read.delim("regressiontest.txt")
> mixed
                     study year ablat mosq1pos mosq1neg mosq2pos mosq2neg
1             Cano et al.  2006     2       42      237      148      629
2 Kerah - Hinzoumbe et al. 2009    10      103     7260        3      215
3            Konate et al. 1994    13       83     5714       48     3609
4           Mwanzia et al. 2011     4        2     8971        0      100

> dat<-escalc(measure="RR", ai = mosq1pos, bi = mosq1neg, ci = mosq2pos, di = mosq2neg, data = mixed, append = TRUE)
> res<-rma(yi, vi, mods = ablat, data=dat)
> predict(res,transf = exp, addx = TRUE)
> preds<-predict(res, transf = exp)
> wi<-1/sqrt(dat$vi)
> size<-0.5 + 3 *(wi-min(wi))/(max(wi)) - min(wi)
> plot(dat$ablat, exp(dat$yi), pch = 19, cex = size, xlab = "Absolute Latitude", ylab = "Relative Risk", las=1, bty = "l", log = "y")
> lines(0:15, preds$pred)

Many thanks,
Charlotte Hewitt




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