How do I measure a portfolio's style factor exposures?

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AcadiFi · Accepted Answer

Two approaches: holdings-based and returns-based. Holdings-based style analysis computes weighted-average factor exposures directly from current holdings. Returns-based style analysis (Sharpe, 1992) regresses the portfolio's returns against returns of style indices under a constraint that weights sum to one and are non-negative.

Holdings example: Riverstone Growth Fund's top 50 holdings have weighted exposures: earnings growth 0.42 (growth tilt confirmed), value -0.38 (anti-value), momentum 0.15, size 0.05, volatility 0.22. Each exposure is the portfolio-weighted average z-score of holdings against a universe.

Returns-based example: regress 36 months of fund returns against Russell 1000 Growth, Russell 1000 Value, Russell 2000 Growth, Russell 2000 Value subject to weights summing to 1 and being between 0 and 1. Optimal weights: 0.70 Russell 1000 Growth, 0.22 Russell 2000 Growth, 0.08 Russell 1000 Value, 0.00 Russell 2000 Value. R² = 93%, so style allocation explains most return variation.

Pros of holdings-based: current, precise, can decompose by sector. Cons: requires holdings data, snapshot can miss turnover.
Pros of returns-based: only needs returns, works for commingled vehicles. Cons: lagging, assumes stable style, constrained to index choice.

Style drift is flagged when exposures or regression weights shift meaningfully quarter-over-quarter. Investment committees require style compliance reporting.

How do I measure a portfolio's style factor exposures?

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