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Ronnie YIN · 2020年01月19日

问一道题:NO.PZ2019103001000042

问题如下:

McLaughlin and Michaela Donaldson, a junior analyst at Delphi, are now discussing how to reposition the portfolio in light of McLaughlin’s expectations about interest rates over the next 12 months. She expects interest rate volatility to be high and the yield curve to experience an increase in the 2s/10s/30s butterfly spread, with the 30-year yield remaining unchanged. Selected yields on the Treasury yield curve, and McLaughlin’s expected changes in yields over the next 12 months, are presented in Exhibit 1.

Donaldson suggests they also consider altering the portfolio’s convexity to enhance expected return given McLaughlin’s interest rate expectations. Donaldson tells McLaughlin the following.

Statement 1 Portfolios with larger convexities often have higher yields.

Statement 2 If yields rise, a portfolio of a given duration with higher convexity will experience less of a price decrease than a similar-duration, lower-convexity portfolio.

Which of Donaldson’s statements is correct?

选项:

A.

Only Statement 1

B.

Only Statement 2

C.

Both Statements 1 and 2

解释:

B is correct.

Statement 2 is correct: If yields rise, a portfolio of a given duration with higher convexity will experience less of a price decrease than a similar-duration, lower-convexity portfolio. Statement 1 is incorrect, as portfolios with larger convexities often have lower yields. Investors will be willing to pay for increased convexity when they expect yields to change by more than enough to cover the sacrifice in yield.

为什么A不选?不是volatility大要选个high convexity

3 个答案

发亮_品职助教 · 2020年02月07日

“题干中提到说int rate volatility是高的,那么statement1改成正确的说法应该是“portfolios with larger convexities often have higher realised return”这样就是对的是吗。yield在任何时候都是专指代bond的ytm吗?”


Hi,Lulu1214可以参考这个回复。

http://class.pzacademy.com/qa/questions/47823

Lulu1214 · 2020年02月02日

题干中提到说int rate volatility是高的,那么statement1改成正确的说法应该是“portfolios with larger convexities often have higher realised return”这样就是对的是吗。yield在任何时候都是专指代bond的ytm吗?

发亮_品职助教 · 2020年01月20日

嗨,爱思考的PZer你好:


不是volatility大要选个high convexity”


是的。当预期收益率曲线波动较大,我们要买High convexity的债券,因为能实现涨多跌少的优势。

但是Statement 1说的不是这个意思。

先说正确的结论是:当预期收益率曲线波动较大时,我们可以增加组合的Convexity,因为Convexity大的组合能享受涨多跌少的优势。

因为,利率跌的时候债券价格涨,两个债券在Duration一致的情况下,Duration衡量两个债券的涨幅一致,但是Convexity大的债券价格会额外涨的更多。这就是Convexity带来的“涨多”。

利率涨的时候债券价格跌,两个债券在Duration一致的情况下,Duration衡量两个债券的跌幅一致,但是Convexity大的债券价格会跌得更少。这就是Convexity带来的“跌少”。

无论利率涨跌,只要利率发生变化,Convexity大的债券表现都会更好。这就是为什么预测收益率曲线波动大时,我们要增加组合的Convexity。

Convexity大的债券,能在利率的变动中,增加债券实现的收益(Realised return)。这是正确的原理。



Statement 1 Portfolios with larger convexities often have higher yields.

而Statement 1的说法是,Convexity大的债券,提供的收益率会更高(Higher)。这里的收益率就是指债券的YTM,即购买债券时,以债券购买价格核算的持有至到期收益率YTM,也就是债券现金流折现时分母上的折现率。

因为Convexity大的债券,在利率变动时有涨多跌少的优势,所以这种债券的价格往往会比较贵,所以其实我们为了更高的Convexity是付出了较高的购买价格。

在债券的现金流既定的情况下、债券的购买价格更高,反算出来的持有至到期收益率YTM(折现率)就越小。

所以买了这种Convexity更大的债券,债券自身带来的收益率会更低。

所以Statement 1错误,他说这种债券带来的收益率会高。Statement 1要改成这样就是正确的:

Portfolios with larger convexities often have lower yields.


虽然这种Convexity大的债券YTM低,但是如果我们预测利率会变,那债券的价格就会呈现“涨多跌少”的优势,所以如果我们不是持有至到期,我们在利率变化后就卖出债券,那这种Convexity大的债券能实现的收益(Realised return)会更高。



总结下:

Statement 1里说的Yield,其实是债券的持有至到期Yield,因为Convexity大的债券卖的贵,所以提供的Yield很低。

而Convexity带来的涨多跌少,实际上是债券的Realised return、是债券投资卖出时实际实现的收益。


换个角度思考,如果我们买了Convexity大的债券,但是利率没有变化,那我们持有至到期的收益会很低,因为期初的购买价高,反算出来的YTM很低。

如果我们买了Convexity大的债券,但是利率波动剧烈,那即便期初核算的持有至到期收益率YTM很低,但因为Convexity大的债券,他们的价格有涨多跌少的优势,我们实现的Capital gain更多、Capital loss更少,所以我们提前卖出债券能实现的Realised return相比就更多。


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