<p>There are four correlation coefficients (cc) which currently lack tags. The point-biserial cc is that between a continuous variable and a binary variable. It is just the Pearson cc between them. There is also the less used rank-biserial cc which is between a ranked variable and a binary. By contrast the biserial cc assumes that the binary variable is the realisation of a latent normal and is an estimate of the correlation of the underlying bivariate normal. The polyserial cc generalises the biserial with an ordered categorical replacing the binary. We currently have 9 question with the word polyserial in them and 39 with the word biserial, most of which seem to be about the point-biserial. Although this is something of a niche area it would seem appropriate to have tags here. I think there are three main options:</p>

<ol>
<li>
Create four tags, one for each cc. This strikes me as overkill
</li>
<li>
Create a tag [biserial] and a tag [polyserial] and tag all the variants of biserial with [biserial]. This seems to me a good option as it does not rely on questionners knowing exactly which biserial they want
</li>
<li>
Create [biserial] and tag all four cc with it. This does not seem quite right to me as the polyserial is not a special case of biserial but rather the other way around
</li>
</ol>

<p>If this meets with general approval I will re-tag them and write the appropriate wiki(s).</p>
