If ex_setting = "401k" then 401k data set is used for (X,Z). Otherwise:
$$Z ~ N_{9}(0,\Sigma),$$
where \(\Sigma_{jj} = 1\), \(\Sigma_{jk} = 0.5\) for all j not equal to k.
$$X = m(Z) + s(Z)*ex,$$
where m and s are step functions of z_1 and z_3 respectively.
$$Y = f(X,Z) + N(0,1).$$