[R] metafor and meta-analysis at arm-level

[Angelo Franchini]

Hello Wolfgang,

Thank you very much for your response.
When you mentionthe "appropriate design matrix", do you mean by that the
'n1i, n2i, m1i, m2i, sd1i, sd2i' arguments of the rma function, or am I
missing something?
I read the documentation on metafor (introduction), rma/rma.uni and
escalc, and that was the only way that I could find for the package to use
information at the arm-level rather than the trial one.

As for the complexity of possible correlations between effects, that is
something to be considered for the network analysis case, correct?

Many thanks.

Best regards,
Angelo



On Sun, July 4, 2010 6:06 am, Wolfgang Viechtbauer wrote:
> Hello Angelo,
>
> You can either supply the arm-level outcomes and corresponding sampling
> variances directly (via the yi and vi arguments) or supply the necessary
> information so that the escalc() or rma() functions can calculate an
> appropriate arm-level outcome (such as the log odds). See the
> documentation of the escalc() function and in particular the part about
> proportions and tranaformations thereof as possible outcome measures.
>
> This is the easy part. Then you need to set up an appropriate design
> matrix to code what arm each observed outcome corresponds to. And finally
> comes the tricky/problematic part. The rma() function assumes independent
> sampling errors and independent random effects for each observed outcome.
> Independent sampling errors is (usually) ok when using arm-level outcomes,
> but the independent random errors part may not be appropriate. This is why
> I am working on functions that do not make this independence assumption.
> With those functions, you can then carry out multivariate and network-type
> meta-analyses. These functions will become part of the metafor package in
> the future.
>
> Best,
>
> --
> Wolfgang Viechtbauer
> http://www.wvbauer.com
>
> "Angelo Franchini" <Angelo.Franchini at bristol.ac.uk> wrote:
>
>>Hi,
>>
>>I have been looking for an R package which allowed to do meta-analysis
>>(both pairwise and network/mixed-treatment) at arm-level rather than at
>>trial-level, the latter being the common way in which meta-analysis is
>>done.
>>By arm-level meta-analysis I mean one that accounts for data provided at
>>the level of the individual arms of each trial and that does not simply
>>derive the difference between arms and do the meta-analysis on that.
>>
>>I am not sure metafor can do that, but hopefully someone more experienced
>>on it can clarify that to me. I can see that it can take data in both
>>forms, arm and trial level, but it looks as if the arm-level information
>>would be converted into trial one through escalc and the latter then used
>>for the meta-analysis. Is that right?
>>
>>Many thanks.
>>
>>Angelo
>>
>>
>>--
>>NIHR Research Methods Training Fellow,
>>Department of Community Based Medicine
>>University of Bristol
>>25 Belgrave Road
>>Bristol BS8 2AA
>>
>>Tel. 0779 265-6552
>>
>>______________________________________________
>>R-help at r-project.org mailing list
>>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.
>
>


-- 
NIHR Research Methods Training Fellow,
Department of Community Based Medicine
University of Bristol
25 Belgrave Road
Bristol BS8 2AA

Tel. 0779 265-6552