Performance Attribution and Investment Alpha › Performance Attribution and Investment Alpha

In the previous chapter, we explored how to measure portfolio performance using metrics like the Sharpe ratio, Treynor ratio, and Jensen's alpha. These measures tell us how well a portfolio performed, but they don't explain why it performed that way. Performance attribution fills this critical gap by decomposing portfolio returns into their underlying sources, allowing us to understand whether outperformance came from smart asset allocation decisions, skilled security selection, or simply exposure to rewarded risk factors.

Performance attribution answers questions that matter deeply to investors and asset allocators: Did our emerging markets allocation add value? Did our technology stock picks outperform or underperform their sector benchmark? How much of our returns came from taking on more market risk versus stock-picking skill? These insights are essential for evaluating investment managers, improving investment processes, and setting appropriate expectations for future performance.

This chapter develops two fundamental attribution frameworks. First, we examine Brinson attribution, which decomposes active returns into allocation and selection effects based on portfolio holdings. Second, we explore factor-based attribution, which uses regression analysis to separate returns into systematic factor exposures (beta) and residual manager skill (alpha). Together, these tools show both the holdings-based and factor-based drivers of portfolio performance.