code: def summary(self):
          
          df = pd.DataFrame(index=self.params_.index)
          df["coef"] = self.params_
          df["se(coef)"] = self.standard_errors_
          df["lower 95% bound"] = self.confidence_intervals_["lower 95% bound"]
          df["upper 95% bound"] = self.confidence_intervals_["upper 95% bound"]
          return df
docs: Summary statistics describing the fit.
  
          Returns
          -------
          df : pd.DataFrame
              Contains columns coef, se(coef), lower, upper
  
          See Also
          --------
          ``print_summary``