[R-meta] Transitivity in a three-level contrast-based network meta-analysis

Natan Gosmann n@t@n@go@m@nn @end|ng |rom gm@||@com
Tue May 5 09:01:59 CEST 2020

Hi everyone,

We are performing three-level models assessing both placebo and medication
effects on continuous outcomes, estimating effect sizes with differences in
standardized mean changes (i.e. we estimate pre-post standardized mean
change of the placebo group and of the medication group. After that, we
calculate the difference among them). These models are being used to
perform a contrast-based (all effect sizes are estimated considering the
placebo group) network meta-analysis and we are including both two-arms
(placebo vs medication) and three-arms (placebo vs medication 1 vs
medication 2) trials.

I have two question concerning the network plot of our study:

1) Considering that all effect sizes are estimated based on placebo groups
and pairwise comparisons among are contrast-based, our network plot should
be star-shaped centered on placebo without any lines between medication
nodes? If so, how should we assess the transitivity assumption of our

2) For three-arms trials, even if we are not estimating the effect sizes
through the head-to-head comparisons, we consider that some degree of
variance is related to the fact that these medication groups are in the
same study. These comparisons should be considered direct effects
(therefore being presented as direct comparisons in the network plot)?

Thank you very much!

Natan Gosmann

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