= Mantel–Haenszel pooled odds ratio
{c}
{title2=$\widehat{\mathrm{OR}}_{\mathrm{MH}}=\frac{\sum_i a_id_i/n_i}{\sum_i b_ic_i/n_i}$}
For independent two-by-two tables with counts $a_i,b_i,c_i,d_i$ and total $n_i$, the Mantel–Haenszel pooled <odds ratio> is the displayed ratio of sums. When all $b_ic_i>0$, it is also the weighted arithmetic mean of study odds ratios with weights $b_ic_i/n_i$. These differ from inverse estimated <variance> weights for <log odds ratios>. Both constructions can represent a <fixed-effect meta-analysis>, but they should not be silently interchanged when interpreting a supplied plot.
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