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<p>Dear Carla,</p>
<p>I think this is a misunderstanding.</p>
<p>R function netmeta() works perfectly with zero standard errors
(by excluding pairwise comparisons with zero or missing standard
errors from the network meta-analysis). This is the same behaviour
as in "basic" meta-analysis of pairwise comparisons (see metagen()
in R package <b>meta</b>). I attached a corresponding fictitious
example for netmeta() to this email.<br>
</p>
<p>The new checks in <b>netmeta</b>, version 0.9-6, you are
referring to, related for <i>treatment arm variances in multi-arm
studies</i> which are calculated internally. Sometimes, users
enter standard errors for pairwise comparisons in multi-arm
studies that simply do not "add up". Accordingly, treatment arm
variances can be negative.</p>
<p>Maybe somebody else can also comment on your idea to use a (very)
small standard error for a pairwise comparison with zero standard
error. In my view, the problem with such an approach is that this
study gets a very large weight in the (network) meta-analysis.</p>
Best wishes,<br>
Guido<br>
<pre class="moz-signature" cols="72">--
Dr. Guido Schwarzer (<a class="moz-txt-link-abbreviated" href="mailto:sc@imbi.uni-freiburg.de">sc@imbi.uni-freiburg.de</a>)
Institute for Medical Biometry and Statistics
Stefan-Meier-Str. 26, D-79104 Freiburg | Phone: +49 (0)761 203 6668
<a class="moz-txt-link-freetext" href="http://www.imbi.uni-freiburg.de">http://www.imbi.uni-freiburg.de</a> | Fax: +49 (0)761 203 6680
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