<p>We have a wealth of questions about cross-validation, such as</p>

<ul>
<li><p><a href="https://stats.stackexchange.com/questions/79905/cross-validation-including-training-validation-and-testing-why-do-we-need-thr">Cross-validation including training, validation, and testing. Why do we need three subsets?</a></p></li>
<li><p><a href="https://stats.stackexchange.com/questions/19048/what-is-the-difference-between-test-set-and-validation-set">What is the difference between test set and validation set?</a></p></li>
<li><p><a href="https://stats.stackexchange.com/questions/188955/is-it-necessary-to-split-dataset-for-cross-validation/188956#188956">Is it necessary to split dataset for cross validation?</a></p></li>
<li><p><a href="https://stats.stackexchange.com/questions/9053/how-does-cross-validation-overcome-the-overfitting-problem/9055#9055">How does cross-validation overcome the overfitting problem?</a></p></li>
<li><p><a href="https://stats.stackexchange.com/questions/1826/cross-validation-in-plain-english">Cross-Validation in plain english?</a></p></li>
</ul>

<p>Which are, if not identical to eachother, do overlap by about 80%. Recently, someone asked the question </p>

<ul>
<li><a href="https://stats.stackexchange.com/questions/204667/cross-validation-purpose-need-and-utility#comment388498_204667">Cross Validation - purpose, need and utility</a></li>
</ul>

<p>Which would seem to overlap with each of those previous threads substantially. The author expressed doubt about many of the threads that I linked to, but I'm not sure that the author's doubt is a great reason to open a new thread which covers highly similar, if not identical, ground as previous threads. This is the same reason we have one canonical thread on the coupon-collector problem, not a separate one for each type of collectible item in existence.</p>

<p>Or, we might look at this from the opposite perspective and say that we have a scattered collection of threads about how cross-validation is used and the problems it does (and doesn't) solve -- but no single, coherent, authoritative thread about cross-validation. I can see two ways to make CV better and more accessible in this regard:</p>

<ol>
<li><p>With malice aforethought, compose a question which fills in the interstitial gaps in our existing questions about CV, and then answer that question deliberately and authoritatively.</p></li>
<li><p>Consolidate existing threads to form a one-stop (or perhaps two-stop) shop of answers about cross-validation.</p></li>
</ol>

<p>I personally favor option 2, since lots of the work has already been done to lay the groundwork of what CV is. Option 1 will create yet another thread about cross-validation and will be harder to find unless it's highly up-voted immediately or you're the Rain Man of the search feature.</p>
