'(cached attribute) dfbetas
uses results from leave-one-observation-out loop'

@cache_readonly
def dfbetas(self):

    dfbetas = (self.results.params - self.params_not_obsi)
    dfbetas /= np.sqrt(self.sigma2_not_obsi[:, None])
    dfbetas /= np.sqrt(np.diag(self.results.normalized_cov_params))
    return dfbetas
