<p><strong>Update (26 Oct 2017): Master tag <a href="https://stats.stackexchange.com/questions/tagged/categorical-encoding" class="post-tag" title="show questions tagged &#39;categorical-encoding&#39;" rel="tag">categorical-encoding</a> has been created, and has the following three synonyms: <code>[dummy-variables]</code>, <code>[indicator-variables]</code>, and <code>[one-hot]</code>.</strong></p>
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<p>I claim that we do need one special tag for (various types) of categorical data encoding/representation in analyses (types are: dummy or one-hot coding, deviation or effect coding, Helmert, repeated, etc. etc.). One omnibus tag for them.</p>
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<p><strong>This suggestion sounds sensible to me.</strong> It got several upvotes (your question + some of the comments) and nobody has objected in the discussion above.</p>
<p>I think it would be good to choose a name that includes &quot;categorical&quot; in it. But <code>[categ-data-encoding]</code> and <code>[categ-coding-scheme]</code> sound too clumsy. Perhaps <code>[categorical-coding]</code>?</p>
<p>Apart from that, I am not a big fan of narrow tags, and I don't like subset tags. So I would be against maintaining further tags that are subsets of this main categorical-coding tag. Therefore:</p>
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<li><p><a href="https://stats.stackexchange.com/questions/tagged/dummy-variables" class="post-tag" title="show questions tagged &#39;dummy-variables&#39;" rel="tag">dummy-variables</a> should be uncoupled from <a href="https://stats.stackexchange.com/questions/tagged/categorical-data" class="post-tag" title="show questions tagged &#39;categorical-data&#39;" rel="tag">categorical-data</a> (I agree with you here), but then made a synonym of our new categorical-coding tag. I don't think we should have it as a separate tag.</p>
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<li><p><a href="https://stats.stackexchange.com/questions/tagged/indicator-variables" class="post-tag" title="show questions tagged &#39;indicator-variables&#39;" rel="tag">indicator-variables</a> (37, no excerpt) should be made synonym of the new categorical-coding tag too. [Note:  many questions currently having this tag are about <em>indicator function</em> and are not at all related to encoding categorical variables for statistical analysis. Those have to be dealt with.]</p>
<p>Update: <a href="https://stats.stackexchange.com/questions/tagged/indicator-function" class="post-tag" title="show questions tagged &#39;indicator-function&#39;" rel="tag">indicator-function</a> was created for questions about indicator function. Along the way, <code>[indicator-variables]</code> has been emptied, so if we want to make it a synonym of categorical-encoding, it has to be re-created first.</p>
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<li><p>We could create <code>[contrast-variables]</code> as another synonym of the same categorical-coding tag if we think it makes sense.</p>
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<li><p>The same goes for <code>[one-hot]</code>: we could create it as another possible synonym of the same tag, it might be useful.</p>
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<p>This way we don't need to decide (see discussion in the comments above) on the terminological details such as whether &quot;dummy variables&quot; can have values other than 0 and 1. We'll have one omnibus tag for all these topics. It will be a subset of <a href="https://stats.stackexchange.com/questions/tagged/categorical-data" class="post-tag" title="show questions tagged &#39;categorical-data&#39;" rel="tag">categorical-data</a>, but perhaps you are right that the topic is important enough to warrant that.</p>
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<p>Just to mention it here: if we go with the above proposal, some manual retagging will be necessary to put this new &quot;coding&quot; tag on the most important threads about encoding categorical variables. As always, we don't need to put it <em>everywhere</em>; it's enough to put it on the most important threads. As far as I understand, @ttnphns volunteered to take care of it.</p>
