[R-meta] Mata-analysis: combining retrospective studies and randomized trials

[Michael Dewey]

Dear Christian

Some comments in-line

On 19/03/2018 10:57, Christian Mirian Larsen wrote:
> Dear all
> 
> My main question is "can retrospective studies and randomized controlled
> trials be combined in a meta-analysis?".
> 
> E.g., I want to investigate the prophylactic effect of antiepileptic drugs
> (AED) given to patients with brain tumors to prevent brain-tumor related
> seizures.
> I have found seven RCT that investigated this subject. Similarly, I have
> found nine retrospective studies examining this topic by going through
> patient records.
> 

I assume the retrospective studies are effectively non-randomised 
trials, having some people who took AED and some not?

> Can I pool the data from the RCT and RS into my matrix (AED/no AED vs.
> seizures/no seizures) and conduct my meta-analysis based on these data?
>

If I were doing that I would also include a moderator variable for study 
type to see if the effect differed depending on it. I would also prepare 
myself for the inevitable comment from referees that the results of the 
non-randomised studies are subject to bias and so should not be compared.

> And lastly, are you familiar to any (epidemiological/biostatistic) studies
> addressing this specific topic on combining RCT and RS?
> 

The issues of having randomised within study comparisons and 
non-randomised ones is often discussed in the context of network 
meta-analysis so that might be the place to look. There were several 
articles in the journal research Synthesis Methods in 2012 starting with 
a general introduction by Salanti starting on page 80 and all in 
sequence from there.

> Thank you in advance
> 
> Regards,
> Christian
> 
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-- 
Michael
http://www.dewey.myzen.co.uk/home.html