<p>@gung recently created the <a href="https://stats.stackexchange.com/questions/tagged/acf-pcf" class="post-tag" title="show questions tagged &#39;acf-pcf&#39;" rel="tag">acf-pcf</a> tag which now has 9 questions: 2 old threads tagged by @gung and 7 new threads (plus 1 migrated to SO). I have two questions about the tag:</p>

<ol>
<li>Do we need it?</li>
<li><del> If we need it, can we at least replace <code>pcf</code> with <code>pacf</code> in the tag name? </del></li>
</ol>

<p><strong>Edit:</strong> 2. Has been done already, only 1. remains relevant.</p>

<p>Regarding <strong>1.</strong>, I think we were doing more or less OK without it. Most of the questions containing ACF and/or PACF I have encountered on CV would ask for </p>

<ul>
<li>identifying an ARIMA structure from ACF/PACF where <a href="https://stats.stackexchange.com/questions/tagged/autocorrelation" class="post-tag" title="show questions tagged &#39;autocorrelation&#39;" rel="tag">autocorrelation</a>, <a href="https://stats.stackexchange.com/questions/tagged/arima" class="post-tag" title="show questions tagged &#39;arima&#39;" rel="tag">arima</a> and <a href="https://stats.stackexchange.com/questions/tagged/model-selection" class="post-tag" title="show questions tagged &#39;model-selection&#39;" rel="tag">model-selection</a> tags are sufficient (IMHO) or</li>
<li>diagnosing problems with a model when some autocorrelation is found in model residuals; there <a href="https://stats.stackexchange.com/questions/tagged/autocorrelation" class="post-tag" title="show questions tagged &#39;autocorrelation&#39;" rel="tag">autocorrelation</a> and <a href="https://stats.stackexchange.com/questions/tagged/diagnostic" class="post-tag" title="show questions tagged &#39;diagnostic&#39;" rel="tag">diagnostic</a> are sufficient (IMHO).</li>
</ul>

<p>If we were to get rid of the tag, it could be </p>

<ul>
<li>made a synonym of <a href="https://stats.stackexchange.com/questions/tagged/autocorrelation" class="post-tag" title="show questions tagged &#39;autocorrelation&#39;" rel="tag">autocorrelation</a> or </li>
<li>just replaced by the above-mentioned tags in the few threads tagged with <a href="https://stats.stackexchange.com/questions/tagged/acf-pcf" class="post-tag" title="show questions tagged &#39;acf-pcf&#39;" rel="tag">acf-pcf</a> but not the ones above, and deleted in other.</li>
</ul>

<p>Regarding <strong>2.</strong>, PACF is the standard acronym of partial autocorrelation function in time series econometrics, while I cannot remember seeing PCF before (though I would not be surprised it exists). On Cross Validated, PACF can be encoutered 670 times while PCF only 17 times. I think having PCF in place of PACF in a tag name may be confusing and may spread the unwarranted use of the nonstandard acronym (so that instead of searching for PACF one will now have to search for both PACF and PCF to capture all the relevant posts).</p>
