The improved model considers not only the relation between certain dependent variables and present value of other ones but also the relation between it and lagged value of all dependent variables.

• 改进后的模型不但考虑到某个因变量与其它因变量当前值的关系，而且考虑到它与所有因变量滞后值的关系，还考虑到它与一些外生变量当前值与滞后值的关系，使模型更加合理。