title: Pandas conversion from object to boolean always returns True using astype
body: <p>I have a column in a dataframe that I need to convert from object to boolean. However, the value changes from <code>False</code> to <code>True</code> when using <code>astype</code>. Any ideas on how to prevent this?</p>
  
  <p><code>df['isgood']</code> returns:</p>
  
  <pre><code>0    True
  1    False
  2    False
  </code></pre>
  
  <p><code>df['isgood'].astype(bool)</code> returns:</p>
  
  <pre><code>0    True
  1    True
  2    True
  </code></pre>