R help - Jul 2016 - metafor estimates using mods and subset do not match

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

I think you should consult with a local statistician. Generally
speaking, statistical questions like this tend to be OT here, and you
appear to be sufficiently confused about the statistical issues that
online posts would not be sufficient.

Cheers,
Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Fri, Jul 29, 2016 at 6:44 AM, Morris, Kathryn <morrisk10 at xavier.edu>
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.

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