docs: def inverse_deriv(self, z):
          """
          Derivative of the inverse of the power transform
  
          Parameters
          ----------
          z : array-like
              `z` is usually the linear predictor for a GLM or GEE model.
  
          Returns
          -------
          g^(-1)'(z) : array
              The value of the derivative of the inverse of the power transform
          function
          """
          return np.power(z, (1 - self.power)/self.power) / self.power