stratified sampling
好像在fixed income 和在equity 里针对asset size情况不一样，一个说适合size大的，一个说适合size小的，还麻烦帮忙梳理一下?以下是我在equity的笔记，但是经典题里我记得有个fixed 厘米是50million，然后又说size太小，stratified不合适？
Stratified sampling is suitable.
1. There has a large number of constituents, or when managing a relatively low level fo assets.
2. Given that the index contains large number of constituents/300, and the manager has only 5million.
