Returns
        -------
            pd.DataFrame of posterior mean  scores vs background

def get_posterior_mean_ratio_scores_vs_background(self):
        '''
        Returns
        -------
            pd.DataFrame of posterior mean  scores vs background
        '''
        df = self.get_term_and_background_counts()
        df['Log Posterior Mean Ratio'] = self._get_posterior_mean_ratio_from_counts(df['corpus'],
                                                                                    df['background'])
        return df.sort_values('Log Posterior Mean Ratio', ascending=False)