<p>To quote from mSO, since my request is <a href="http://meta.stackexchange.com/q/192195/189912">pretty much identical</a>:</p>

<blockquote>
  <p>I would like to have statistics for the quality of posts coming from
  unregistered versus registered accounts on my site.</p>
  
  <p>It is my suspicion that people who are willing to put out the effort
  to register an account will also put more effort into writing good
  questions; I'd like to see some evidence for or against this.</p>
  
  <p>I also suspect that on my site the vast majority of good questions and
  answers come from registered users, but again I'd like to see some
  data.</p>
  
  <p>Is this already possible through the Data Explorer?  If so, how?  If
  not consider this a feature request.</p>
</blockquote>

<p>The reason for this is I am considering proposing that Server Fault stop accepting questions from unregistered users, and I would like to have statistics to analyze as part of that process.</p>