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However, only for Portfolio Z can we say there is strong proof that performance in the corporate
spread risk was achieved. Thus, the concern of committee member #2 is valid due to differences
in performances for the corporate credit products.
(c) Committee member 3: “It seems that managers X and Z were able to outperform the
benchmark without taking on any interest rate risk at all.”
Interest rate risk is captured by the yield curve risk factor, while non-interest rate risk is captured
by the other five risk factors. As seen below, it does appear that committee member #3 is correct
However, what the above breakdown does not include are the individual components of yield
curve risk (level and shape risks). This is explained in more detail below.
Factor-based attribution models actually allow a decomposition of the yield curve risk into level
(duration) risk and changes in the shape of the yield curve. For example, for the three portfolios
just discussed, suppose that the attribution due to yield curve risk is determined to be as follows:
Notice that once yield curve risk is decomposed as shown above, it turns out those managers of
Portfolios X and Z did indeed make interest rate bets on both level risk and shape risk. It turns
out that the two bets almost offset each other so there were only small basis point returns
attributable to the interest rate bets. It appears that Portfolio Z’s manager made a major duration
bet and a minor bet on changes in the shape of the yield curve. Thus, as it turns out, committee
member #3 was incorrect as managers of Portfolios X and Z were making greater interest rate
bets than that of Portfolio Y. Thus, given the above breakdown of yield curve risk, their
performance was not all related to their lack of interest rate bets. We one cannot make definitive
conclusions about portfolio managerial performance in terms of interest rate bets without a more
detailed analysis.