[R] metafor estimates using mods and subset do not match

[Morris, Kathryn]

I am running a meta-analysis using metafor and getting what seem to be conflicting results.

#analysis with species moderator 
cropMeta.species<-rma(cropyi, cropvi, data=dataCropMeta, mods=~dataCropMeta$species - 1, method="HE")

The output for the analysis using species as a moderator shows estimates for the seven species in my data set, and makes sense.

#subset analysis with B oleraceae
cropMeta.species.b.oleracea<-rma(cropyi, cropvi, data=dataCropMeta, subset=(species=="B. oleracea"), method="HE")

Then when I start to plot the results and use separate analyses for each species in order to get the coef and variances for plotting the subgroups I get different estimates. The estimates for most subgroups are almost identical in both analyses, but one of them is 5.922 in the analysis with species as a moderator, and 7.0139 in the subset analysis for only that species.

Why are the estimates different? If they should be different, then which analysis is producing the correct estimates?

I'm happy to provide the data and R scripts if that would help.

many thanks,
Kathryn  
 
 
---------------------------------

 Dr. Kathryn Morris
 Assistant Professor, Biology
 Xavier University
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 Cincinnati, OH
 45207

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