'Significance test for the variables in the regression.
Parameters
var_pos: sequence
The position of the variable in exog to be tested.
Returns
sig: str
The level of significance:
- `*` : at 90% confidence level
- `**` : at 95% confidence level
- `***` : at 99* confidence level
- "Not Significant" : if not significant'

def sig_test(self, var_pos, nboot=50, nested_res=25, pivot=False):

    var_pos = np.asarray(var_pos)
    (ix_cont, ix_ord, ix_unord) = _get_type_pos(self.var_type)
    if np.any(ix_cont[var_pos]):
        if (np.any(ix_ord[var_pos]) or np.any(ix_unord[var_pos])):
            raise ValueError('Discrete    variable    in    hypothesis.    Must    be    continuous')
        Sig = TestRegCoefC(self, var_pos, nboot, nested_res, pivot)
    else:
        Sig = TestRegCoefD(self, var_pos, nboot)
    return Sig.sig
