<p>We have <a href="https://stats.stackexchange.com/questions/tagged/nested" class="post-tag" title="show questions tagged &#39;nested&#39;" rel="tag">nested</a> with 216 Qs and also <a href="https://stats.stackexchange.com/questions/tagged/non-nested" class="post-tag" title="show questions tagged &#39;non-nested&#39;" rel="tag">non-nested</a> with 22 Qs. Neither tag has a wiki excerpt. Both are terribly ambiguous.</p>

<p>AFAIK, "nested" can refer (and this tag <em>is</em> being used to refer) to various conceptually different things that have little to do with each other:</p>

<ol>
<li>Nested data / nested experimental design (nested factors in ANOVA, nested random effects in mixed models, etc.)</li>
<li>Nested models (e.g. doing LR test on two nested models)</li>
<li>Nested cross-validation</li>
</ol>

<p><strong>Update April 2016:</strong> I looked through the last 50 threads tagged with [nested]. 39 are about nested data (split ~50:50 between ANOVA and mixed models); 1 is about nested models; 10 are about nested cross-validation. Among the [non-nested] threads, most seem to be about nested models.</p>

<p>I suggest to split these two tags into three new tags, corresponding to the above categories.</p>

<p><strong>Questions:</strong></p>

<ol>
<li><p>Would <code>[nested-data]</code> be an okay name for nested anova/lmer stuff? We could have nested-anova, nested-random-effect, nested-factor as synonyms. There is also a <code>[multilevel-analysis]</code> tag, but people asking about nested anova do not usually use this terminology...</p></li>
<li><p><code>[nested-models]</code> would do, wouldn't it?</p></li>
<li><p>Do we need <code>[nested-cross-validation]</code> tag, or can we retag these threads to <code>[cross-validation]</code> and that's it?</p></li>
</ol>
