定義
Beta measures how sensitively an investment's returns move relative to a reference market — typically expressed as a number where 1.0 means the investment moves in line with that market.
Beta is a measure of systematic risk — the risk tied to broad market movements rather than a specific company or manager decision. A beta above 1.0 suggests the investment has historically amplified market swings in both directions; a beta below 1.0 suggests it has dampened them. A beta near zero implies returns have been largely unrelated to the reference market's movement.
For wealthy families, beta is a foundational input in understanding what a portfolio actually owns at a risk level. Consider a hypothetical family whose portfolio holds a dozen different funds. If most of those funds carry high equity beta, the portfolio may feel diversified by name while behaving like a single concentrated equity bet during a market downturn. Mapping beta exposures is a step toward genuine diversification.
A critical nuance: beta is always measured relative to a specific index over a specific time period. The same investment can show different betas depending on the reference index chosen and the lookback window used. This makes beta a useful approximation, not a precise permanent attribute. It is also worth noting that beta describes past behavior; future sensitivity can shift as a company's business model or capital structure changes. Understanding beta is central to risk budgeting and to evaluating asset allocation decisions.
最終レビュー日 August 25, 2026 · 編集方針