title: What is there a factor of 3 in Pearson's 2nd skewness (median skewness)
body: <p>I've been searching for this and I cannot seem to find an easy answer.  Can someone please explain why there is a factor of three is Pearson's second skewness coefficient (median skewness).</p>
  
  <p><a href="https://en.wikipedia.org/wiki/Skewness" rel="nofollow">https://en.wikipedia.org/wiki/Skewness</a></p>
  
  <p>It is defined as:</p>
  
  <pre><code>3*(mean-median)/std_dev
  </code></pre>
  
  <p>The</p>
  
  <pre><code>(mean-median)/std_dev
  </code></pre>
  
  <p>makes sense, as it is a measure of how much the median is away from the mean compared to the standard deviation, but Pearson's coefficient adds a factor of 3.  I'd like to know why this is, and why or why not this is a better measure than simply:</p>
  
  <pre><code>(mean-median)/std_dev
  </code></pre>