[R-meta] Violation in non-independece of errors (head to head studies and mutlilevel meta-analysis)?

[Natan Gosmann]

 Hello all,

We are conducting a large multilevel meta-analysis using the metafor
package considering all RCTs that assessed medications vs placebo for
psychiatric disorders.

We included all available outcomes from each study and therefore, we are
considering study and assessment instrument (scale) as random variables in
the model. The yi comes from differences in standardized mean change
between medication and placebo for each study.

We are trying to avoid network meta-analysis, given we want our results to
be adjusted by several moderators that affect antidepressant response.

However, we have doubts about how we can handle head to head studies
(studies with more than one medication) and studies with distinct dosages
of the same medication. We were thinking to just calculate differences from
placebo (but placebo would be the same group for those studies - would be
the contrast group for more then one medication or dosage group). Including
study ID as random variable already accounts for violation in
non-independence of errors? Is that an appropriate way of doing that?

Alternatively, should we select only one medication from head to head
trials?

I would very much appreciate if you could help us with that.

Best regards,
Natan


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