'Returns the standard errors of the variance parameters.  Note
that the sampling distribution of variance parameters is
strongly skewed unless the sample size is large, so these
standard errors may not give meaningful confidence intervals
of p-values if used in the usual way.'

@cache_readonly
def bse_re(self):

    p = self.model.exog.shape[1]
    return np.sqrt((self.scale * np.diag(self.cov_params())[p:]))
