docs: def deviance(self, endog, mu, freq_weights=1., scale=1.):
          """
          Gaussian deviance function
  
          Parameters
          ----------
          endog : array-like
              Endogenous response variable
          mu : array-like
              Fitted mean response variable
          freq_weights : array-like
              1d array of frequency weights. The default is 1.
          scale : float, optional
              An optional scale argument. The default is 1.
  
          Returns
          -------
          deviance : float
              The deviance function at (endog,mu,freq_weights,scale)
              as defined below.
  
          """
          return np.sum((freq_weights * (endog - mu)**2)) / scale