Alpha That Is Really Beta in Disguise

Every year, someone presents a strategy with a beautiful Sharpe ratio that turns out, on inspection, to just be a small-cap tilt, or a short-vol bet, or leveraged momentum, relabeled. This is not usually dishonest — it is what happens when a signal is validated only against a flat benchmark instead of against the risk factors it is quietly correlated with. The strategy is not fake. It is just not what the researcher thinks it is.

Why this happens so easily

A cross-sectional signal built from, say, low analyst coverage will tend to load on small size, because small stocks are undercovered. A signal built from recent price strength will load on momentum. Neither loading is a bug in the signal-construction code; it is a real, mechanical relationship between the signal and a well-known factor. The trouble is that "well-known factor" means the return is not new information about mispricing — it is compensation for a risk the market has already priced, that thousands of other funds are also collecting. Calling it alpha overstates how much the research contributed and understates how correlated the strategy is with everything else in the book.

The check that catches it

Regress the strategy's returns on a standard factor set — market, size, value, momentum, quality, low-vol, whatever the shop's model uses — and look at what's left over, the residual. If the loadings on known factors explain most of the return and the leftover (the true alpha) is statistically indistinguishable from zero, the "edge" was beta wearing a costume. If a meaningful, significant residual remains after the known factors are accounted for, there is a real claim to novelty — though even then, the honest caveat is that it may simply be a factor nobody has named yet, not necessarily true idiosyncratic skill.

Signal you think you built	Factor it often turns out to load on
Low analyst coverage	Small size
Recent 6–12 month price strength	Momentum
High earnings yield	Value
Low realised volatility	Low-volatility / quality
Recent IPO underperformance	Small size, illiquidity

A worked example

A researcher builds a "quality" signal from return-on-equity and finds an annualised Sharpe of 1.1 gross. Running the strategy's return series against a five-factor model shows a market beta of 0.15, a size loading of −0.4 (it's short small caps), and a quality-factor loading of 0.9. After removing the contribution of those three exposures, the residual return has a t-stat under 1. The signal was, almost entirely, a leveraged bet against small caps expressed through a quality screen — not new information, a repackaging of exposures the market already prices.