[R-meta] Network meta-analysis: including a within-person (split-leg) study + pooling absolute vs relative changeNetwork meta-analysis: including a within-person (split-leg) study + pooling absolute vs relative change

[Viechtbauer, Wolfgang (NP)]

Hi Jorge,

Much more readable!

I see no inherent problem with including study IV, but not sure why you structured it as you did. In essence, it is like this:

           Obs     Tx A    Tx B    Tx C
Study I      1       100     150       -
Study II     1       200       -     200
Study III    1       200     200       -
Study IV     1         -     170     180

But since study IV is a within-subjects design, the two means are not independent. So you would have to compute the covariance between them and include this in the V matrix. The covariance between the two means is a function of the correlation of the raw measurements for the two legs. If this is not reported, then you could use a guestimate and do a sensitivity analysis.

Best,
Wolfgang

> -----Original Message-----
> From: R-sig-meta-analysis <r-sig-meta-analysis-bounces using r-project.org> On Behalf
> Of Jorge Teixeira via R-sig-meta-analysis
> Sent: Wednesday, October 28, 2026 10:57
> To: Michael Dewey <lists using dewey.myzen.co.uk>; R meta <r-sig-meta-analysis using r-
> project.org>
> Cc: Jorge Teixeira <jorgemmtteixeira using gmail.com>
> Subject: Re: [R-meta] Network meta-analysis: including a within-person (split-
> leg) study + pooling absolute vs relative changeNetwork meta-analysis: including
> a within-person (split-leg) study + pooling absolute vs relative change
> 
> Thanks, Michael. And now?!
> 
> I'm planning a small network meta-analysis and would value your
> input on two design questions.
> 
> SETUP
> 
> I have three parallel-group RCTs comparing treatments A, B and C
> (mean value at post per arm):
> 
>               Tx A    Tx B    Tx C
>   Study I      100     150       -
>   Study II     200    200      -
>   Study III      -     200     200
> 
> I would like to add a fourth study (Study IV). It is a within-person
> design: each participant's legs were randomized to different
> treatments, so comparisons are within-group rather than
> between-group. I have the post-treatment means + SD for each
> condition.
> 
> QUESTION
> 
> Can Study IV be meta-analyzed together with the three parallel RCTs?
> 
>             Obs     Tx A    Tx B    Tx C
>   Study I      1       100     150       -
>   Study II     1       200       -     200
>   Study III    1       200     200       -
>   Study IV     1         -       -     180
>   Study IV     2         -     170       -
> 
> Thanks a lot for your help.
> 
> Best,
> Jorge
> 
> On Wed, 28 Oct 2026 at 09:12, Michael Dewey <lists using dewey.myzen.co.uk> wrote:
> >
> > Dear Jorge
> >
> > You have set your mailer to post in HTML which mean that we are not
> > seeing what you posted. Not sure how you get plain text.
> >
> > I think the answer to question 2 is No. It is fairly easy to create
> > examples with the same absolute change and different relative change.
> >
> > Michael