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st: RE: Question regarding Trim and Fill method using 'metatrim'


From   "Tiago V. Pereira" <tiago.pereira@mbe.bio.br>
To   statalist@hsphsun2.harvard.edu
Subject   st: RE: Question regarding Trim and Fill method using 'metatrim'
Date   Sun, 5 Sep 2010 15:26:16 -0300 (BRT)

Dear Chan,

If I got the big picture correctly, your results seem to be OK: the
command is correct and the results are intuitive.

Firstly, as the test for small-study effects indicates that there is no
substantial bias, it is reasonable to expect some agreement between it and
the 'trim and fill' approach. In other words, there is no reason to expect
the trim and fill to adjust for publication bias if it in fact doesn't
exist. If you have raw data (i.e. 2x2 tables), try to investigate small
study effect using the Harbord's test as well (metabias a b c d, harbord)

Secondly, I would be very concerned to use the trim and fill approach in
results showing strong evidence for statistical heterogeneity. This seems
to be the case in your data set of 13 studies: Q= 41.214 (12 df) and
estimated tau^ =  0.023. To understand the problem, see:

http://www.ncbi.nlm.nih.gov/pubmed/12820277
http://www.ncbi.nlm.nih.gov/pubmed/17476644

Thirdly, visual inspection of the funnel plot is highly subjective with 13
studies only. Indeed, the asymmetry in the funnel plot that you see may be
either entirely subjective or a result of the statistical heterogeneity
across study results.

hope this helps.

Tiago



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