[求助]关于IR=IC*(breadth)^0.5

challenge, produce, advantage, obtaining, investment

1.首先请问原版书285页第10题的答案说(比较stock - based enhanced indexing 于 Synthetic enhanced indexing)： Stock - based enhanced indexing's advantage is: greater breadth than synthetic approach. That said, as with all active strategies, obtaining a satisfactory IC or level of investment insight is the challenge. Synthetic enhanced indexing has narrower breadth (usually a duration or credit bet) and so requires a high IC to produce the same level of IR. 请问这句话怎么理解。为什么stock based enhanced indexing比synthetic 的breadth 高，这里的breadth是指可以试错做ReBalancing的机会么？另外IC 究竟怎么理解？比如再看284页第8题的答案：大意是说如果把 active risk增加一倍，很难把active return增加一倍。因为这样就意味 IR保持不变。而实际上，即使 breadth 不变， IC (Insight) 也会下降。怎么理解？我觉得对于同一种asset class,你的知识不变， insight一样的哦，即使说可能市场上能发掘的机会相对少，但是多花时间，总是可以保持IC不变啊？中而言之，我的问题是，哪些因素会分别导致IC 和 breadth改变？ 1. active risk? 2. 练习投资的次数？ 3.学习的时间？4.样本量？