Cross-sectional alpha (also called relative-value alpha) is measured by ranking assets within a universe on a signal at time t and predicting which will outperform or underperform each other over the subsequent return horizon — not whether the universe as a whole rises or falls.
A cross-sectional strategy is typically market-neutral: by going long the top-ranked assets and short the bottom-ranked, systematic market exposure is hedged out, leaving alpha net of the common factor.
Contrast with time-series alpha
- Time-series alpha — predicts whether a single asset's return will be above or below its own historical average (e.g., a momentum signal applied to a single futures contract).
- Cross-sectional alpha — predicts the ordering of returns across a universe at a given time. The IC is inherently a cross-sectional concept.
Most equity long-short strategies operate on cross-sectional alpha. The Fundamental Law of Active Management — and the role of breadth — applies primarily to the cross-sectional context.