The Fundamental Law of Active Management and Alpha Research
Summary
This article introduces alpha and beta through market and multifactor models, describing alpha as return unexplained by modeled risk exposures. It explains how active portfolios might seek positive alpha while keeping factor exposures aligned with a benchmark, or hedge market exposure when a stable source of alpha is believed to exist. Information ratio is presented as risk-adjusted active performance, while the information coefficient measures the cross-sectional association between forecasts and subsequent returns.
The Fundamental Law framework links information ratio to forecast skill and the breadth and independence of opportunities. A related heuristic expresses alpha in terms of return volatility, information coefficient, and a standardized asset score. The article suggests testing factors through historical predictive correlations and ranking assets by useful signals. It cautions that factor predictive power changes over time, factor timing is difficult, and high variability in information coefficients creates model risk. These relationships rely on simplifying assumptions, and the text offers a conceptual framework rather than a fully specified portfolio or empirical test.
Key ideas
- Alpha is the return not explained by modeled systematic risk exposures.
- Information ratio measures active return relative to its variability, while information coefficient measures forecast association with realized returns.
- The Fundamental Law relates strategy breadth and forecast skill to potential information ratio.
- A heuristic decomposes alpha into volatility, predictive skill, and the strength of an asset score.
- Factor predictive power can vary over time, making factor selection and timing uncertain.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.