title: Statsmodel .predict omits or deletes records
body: <p>I am sampling a larger data set to fit and predict with a statsmodels GLM model.  </p>
  
  <p>Depending on the sample, running <code>model.predict</code> will omit some small number (&lt;10) of records in the array that it returns.  I assume it experiences some error in processing some small number of the rows in the data set. </p>
  
  <p>For instance, if I predict using rows 15000:20000, the shape of the array returned will be 4994, or 4997, or something similar.</p>
  
  <p>This is a pain because I can't tell which rows are omitted, and I would like to run the .predict function on the entire dataframe and then easily add the prediction values as a new column.</p>
  
  <p>Does someone either (a) know what's going on and how to fix it, or (b) have a good method for adding the prediction values back to the dataframe based on index?</p>