title: Percentile rank calculation
body: <p>I'm attempting to calculate the <a href="http://en.wikipedia.org/wiki/Percentile_rank" rel="noreferrer">percentile rank</a> of a score using the <a href="http://code.google.com/p/python-statlib/" rel="noreferrer">python statlib</a> module. The <em>percentileofscore</em> function is supposed to return a value between 0 and 100, however it regularly produces numbers outside this range. An example:</p>
  
  <pre><code> &gt;&gt; a = [0,1,2,3,4,5]
   &gt;&gt; percentileofscore(a, 0)
   108.33333333333333
  </code></pre>
  
  <p>I've tried the <a href="http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.percentileofscore.html" rel="noreferrer">scipy</a> module, and have also rolled my own with similar results.</p>
  
  <p>Am I misunderstanding something re. this function?</p>
  
  <p>EDIT - More examples:</p>
  
  <pre><code> percentileofscore([23,23,23,25], 23)
   137.5
   percentileofscore([12,19,65,25], 12)
   112.5
   percentileofscore([112,109,605,25], 25)
   112.5
  </code></pre>
  
  <p>Seems that querying the percentile of the lowest score causes the problem. A bug perhaps?</p>