How do you decompose a bond portfolio's total return into its component sources using fixed income attribution analysis?
I'm studying CFA Level III portfolio management and the return attribution for bonds seems more complex than for equities. There are income, Treasury curve, spread, and selection effects. Can someone walk through each component with a concrete example?
Fixed income return attribution decomposes a bond portfolio's total return into distinct sources, allowing investors to evaluate which decisions added or subtracted value. Unlike equity attribution (which focuses on sector and stock selection), bond attribution must account for the unique drivers of fixed income returns.
The Attribution Framework:
Total Return = Income Effect + Treasury Curve Effect + Spread Effect + Selection Effect + Residual
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Worked Example:
Crestfield Bond Fund returned 3.85% over the past year. The benchmark (Bloomberg US Aggregate) returned 3.10%.
1. Income Effect (+1.42%)
- Portfolio yield: 4.15% (vs benchmark 3.78%)
- Rolldown return: As bonds age, they move down the yield curve, earning additional return
- Portfolio rolldown: +0.22% vs benchmark +0.18%
- Income contribution above benchmark: (4.15% + 0.22%) - (3.78% + 0.18%) = +0.41%
2. Treasury Curve Effect (+1.28%) Measured by repricing each bond using the new Treasury curve while holding spreads constant.
- Portfolio duration was 6.8y vs benchmark 6.2y
- Treasuries rallied ~20 bps across the curve
- Duration overweight captured: (6.8 - 6.2) x 0.20% = +0.12% above benchmark
3. Spread Effect (+0.91%) Measured by repricing each bond using the change in its OAS.
- Portfolio was overweight BBB corporates (spread duration 5.1y vs 4.3y)
- BBB spreads tightened 15 bps
- Spread contribution: (5.1 - 4.3) x 0.15% = +0.12% above benchmark
4. Selection Effect (+0.19%) Residual security-level outperformance after accounting for systematic factors. Reflects credit analyst skill in choosing individual issuers.
Key Insights for the Exam:
- Income effect is typically the largest and most stable component
- Treasury effect measures duration and curve positioning skill
- Spread effect captures sector allocation and credit quality timing
- Selection effect isolates bottom-up security picking
- A manager can outperform through any combination of these channels
Dive deeper into attribution models in our CFA Fixed Income course.
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