title: how is pandas kurtosis defined?
body: <p>I am trying to get kurtosis using pandas. By doing some exploration, I have</p>
  
  <pre><code>test_series = pd.Series(np.random.randn(5000))
  test_series.kurtosis()
  </code></pre>
  
  <p>however, the output is:</p>
  
  <pre><code>-0.006755982906479385
  </code></pre>
  
  <p>But I think the kurtosis (<a href="https://en.wikipedia.org/wiki/Kurtosis" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Kurtosis</a>) should be close to (maybe normalize over N-1 instead of N, but this does not matter here)</p>
  
  <pre><code>(test_series - test_series.mean()).pow(4).mean()/np.power(test_series.std(),4)
  </code></pre>
  
  <p>which is </p>
  
  <pre><code>2.9908543104146026
  </code></pre>