Can you explain why "persistence" of export sales ratio ( and import sales ratio as well)  to be of importance in studing the sources of comparative advantage??

想了很久，没有思路。

唯一想到的就是或许它trace long run characteristic of international trade.

请大家帮我看看，讨论一下，也请高人留步，指点一下，多多多谢。

[此贴子已经被作者于2009-1-10 4:02:30编辑过]