Beta: how closely a security repeats the market

Beta shows how strongly a security moved with the market in the past.

How to read it

A value near one means the security tracked the market. Above one it amplified the market's moves; below one it damped them.

A negative value would mean moving against the market; in practice that is rare and usually unstable.

What to do with it

Judge how far a portfolio depends on the market as a whole. A portfolio of high-beta securities falls harder than the index in a bad period — a property worth knowing in advance.

Compare results honestly: beating the index with a high beta is not an achievement but a consequence of taking more risk — The benchmark: what to compare your result against honestly.

What it does not measure

Company-specific risk: an accident, a corporate conflict, a regulatory decision. Those events are unrelated to the market, and beta says nothing about them.

That is exactly why beta is a measure of market risk rather than of risk in general — Volatility is not risk.

Where it is used

In hedging: sizing a protective position requires an estimate of the portfolio's sensitivity to the market — Hedging: insurance paid for with return.

In sector analysis: cyclical industries carry a higher beta — Economic cycles: why downturns repeat.