<p><strong><em>Return back to the issue, June 30, 2017</em></strong></p>

<p>I want to bring your attention once again to this tag question about categorical data encoding. It has not been resolved satisfactory so far, to me.</p>

<p>1) I claim that we <strong>do need</strong> 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. Just imagine it: we have endemic tag <code>[many-categories]</code> but we don't have a tag for ubiquitous theme of how to represent categorical variables in this or that analysis or situation. We have currently only tag <code>[categorical-data]</code> which covers it but is <em>much more broad</em> and general.</p>

<p>So, I recommend to create the tag. Wording candidates: <code>[contrast-variables]</code> or <code>[categ-data-encoding]</code> or <code>[categ-coding-scheme]</code> or suggest your variant.</p>

<p>2) <strong>Dummy</strong> (aka one-hot) binary variables are the most well-known type of the categorical encoding / contrast variables. As currently, the tag <code>[dummy-variables]</code> is a slave synonym to <code>[categorical-data]</code>. Please recover it back as the tag on its own. Next thing: we yet keep currently separate tag <code>[indicator-variables]</code> however. This is strange because it is conceptually the same thing as dummy variables (just less known term).</p>

<p>So, either map <code>[indicator-variables]</code> to the restored <code>[dummy-variables]</code> as its junior synonym; or, if you prefer <code>[indicator-variables]</code>, keep it, but then map <code>[dummy-variables]</code> to it (not to <code>[categorical-data]</code>).</p>

<hr>

<p><strong><em>Original post Mar 6, 2017:</em></strong></p>

<p>Please, consider these opportunities. Agree, disagree, your suggestions...</p>

<p><strong>Moderators</strong>, please remove <code>[dummy-variables]</code> tag from being a synonym to <code>[categorical-data]</code>. These are definitely not synonyms. Categorical data can be represented as dummy variables, sure. That doesn't make the two concepts same at all.</p>

<p><code>[dummy-variables]</code> should be kept a separate tag, and <code>[indicator-variables]</code> be made its junior synonym. In a recent <a href="https://stats.meta.stackexchange.com/q/4668/3277">question</a>/comment I've expressed my tendency to see indicators as a synonym of dummy. "Dummy", in turn, is just the binary type of "contrast variables", not any contrast variables.</p>

<p>Therefore tag <code>[contrast-variables]</code> should be created. It is elementary variables to which categorical data (factors) are recoded, explicitly or implicitly, in ANOVA-like procedures. Contrast variables correspond, but not synonymic, to <code>[contrasts]</code> (comparing combinations of coefficients, we do have this tag already). Contrast variables include types "dummy", "deviation / effect", "Helmert", and so on.</p>

<p>If people agree and moderators recover <code>[dummy-variables]</code> I could then proceed and fix the tagging of questions according to the above thesaurus.</p>

<hr>

<p>So far I can see these three alternatives:</p>

<ul>
<li><p>define <code>[dummy-variables]</code> (or <code>[dummy-set]</code>) as binary indicator variables obtained out of a categorical variable. &amp; create <code>[contrast-variables]</code> (or <code>[contrast-set]</code>) as more general - not necessarily binary - such variables (I vote for this variant)</p></li>
<li><p>define <code>[indicator-variables]</code> (or <code>[indicator-set]</code>) to be what "dummy variables" was defined just above. &amp; define <code>[dummy-variables]</code> (or <code>[dummy-set]</code>) to be what "contrast variables" was defined just above.</p></li>
</ul>

<p>Both variants require <code>[dummy-variables]</code> to be restored as a proper tag. </p>

<ul>
<li>Third solution: don't restore/define anyhow old <code>[dummy-variables]</code> tag, however create tag <code>[contrast-variables]</code> which, if you like, we may give another name, say <code>[categ-coding-scheme]</code>.</li>
</ul>
