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

[Michael Dewey]

Dear Kathryn

I think that the author of metafor has addressed this

http://www.metafor-project.org/doku.php/tips:comp_two_independent_estimates

The other tips on that site are well worth reading too.

On 29/07/2016 14:44, Morris, Kathryn wrote:
> 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
>  3800 Victory Parkway
>  Cincinnati, OH
>  45207
>
>  Office: (513) 745-3554
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>

-- 
Michael
http://www.dewey.myzen.co.uk/home.html