'Heteroskedasticity-consistent parameter covariance
Used to calculate White standard errors.'

@property
def wrnorm_cov_params(self):

    if (self._wncp is None):
        df = self.df_resid
        pred = np.dot(self.wexog, self.coeffs)
        eps = np.diag(((self.wendog - pred) ** 2))
        sigmaSq = np.sum(eps)
        pinvX = np.dot(self.rnorm_cov_params, self.wexog.T)
        self._wncp = ((np.dot(np.dot(pinvX, eps), pinvX.T) * df) / sigmaSq)
    return self._wncp
