'Returns the confidence intervals of the marginal effects
Parameters
alpha : float
Number between 0 and 1. The confidence intervals have the
probability 1-alpha.
Returns
conf_int : ndarray
An array with lower, upper confidence intervals for the marginal
effects.'

def conf_int(self, alpha=0.05):

    _check_at_is_all(self.margeff_options)
    me_se = self.margeff_se
    q = norm.ppf((1 - (alpha / 2)))
    lower = (self.margeff - (q * me_se))
    upper = (self.margeff + (q * me_se))
    return np.asarray(lzip(lower, upper))
