<p>Around a month ago, @gung suggested to make <a href="https://stats.stackexchange.com/questions/tagged/nominal" class="post-tag" title="show questions tagged &#39;nominal&#39;" rel="tag">nominal</a>×113 a synonym 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>×1987 because they are "literally synonyms". This has  initially gotten some support, until @ttnphns objected on the grounds that <a href="https://stats.stackexchange.com/questions/tagged/ordinal-data" class="post-tag" title="show questions tagged &#39;ordinal-data&#39;" rel="tag">ordinal-data</a>×531 is also "categorical": nominal and ordinal, he says, are two sub-types of categorical data, and therefore we should leave all three tags separate. The whole discussion is here in the comments: <a href="https://stats.meta.stackexchange.com/a/4717/28666">https://stats.meta.stackexchange.com/a/4717/28666</a>.</p>

<p><strong>I feel that we need to arrive to some decision here.</strong></p>

<ul>
<li><p>Option #1 (@gung): map <a href="https://stats.stackexchange.com/questions/tagged/nominal" class="post-tag" title="show questions tagged &#39;nominal&#39;" rel="tag">nominal</a> to <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>. To be consistent, this would require looking through <code>categorical-data</code> threads and moving the ones about ordinal data to <a href="https://stats.stackexchange.com/questions/tagged/ordinal-data" class="post-tag" title="show questions tagged &#39;ordinal-data&#39;" rel="tag">ordinal-data</a>. A quick search <a href="https://stats.stackexchange.com/search?tab=votes&amp;q=%5bcategorical-data%5d%20ordinal%20is%3aquestion"><code>[categorical-data] ordinal is:question</code></a> yields 166 Qs, and not all of them would need to be retagged, so we are probably talking about minority of questions, perhaps ~100.</p></li>
<li><p>Option #2 (@ttnphns): do not make any synonyms. (But I'd suggest to rename <a href="https://stats.stackexchange.com/questions/tagged/nominal" class="post-tag" title="show questions tagged &#39;nominal&#39;" rel="tag">nominal</a> into <a href="https://stats.stackexchange.com/questions/tagged/nominal-data" class="post-tag" title="show questions tagged &#39;nominal-data&#39;" rel="tag">nominal-data</a> for consistency).</p></li>
</ul>

<p>In either case we will need to edit the wikis and wiki excerpts to clarify the usage. At the moment some information there is conflicting, e.g. wiki for <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> says </p>

<blockquote>
  <p>categorical values are considered as abstract entities without any mathematical structure such as an order or a topology [written by @whuber in 2012]</p>
</blockquote>

<p>but its wiki excerpt says</p>

<blockquote>
  <p>Some people consider ordinal scale categorical too [written by @ttnphns in 2013]</p>
</blockquote>
