Calculating and Interpreting Market Beta from Returns

Summary

The document explains beta as an asset’s sensitivity to market returns and gives the covariance of asset and market returns divided by market-return variance as its calculation. It illustrates the calculation with a short set of monthly portfolio and benchmark returns, reporting a beta of about 1.09 and interpreting it as somewhat greater market sensitivity.

It describes how positive, zero, and negative beta values are commonly interpreted, including the idea that beta above one tends to magnify market moves while beta below one tends to dampen them. These examples are simplified: beta measures historical co-movement relative to a chosen benchmark and does not guarantee that an asset will move by a fixed multiple in future markets. The document does not discuss estimation uncertainty, the choice of lookback period, or differences across benchmarks.

Key ideas

• Beta is calculated as asset-market return covariance divided by market return variance.
• A beta above one indicates stronger historical sensitivity to benchmark moves, while a beta below one indicates weaker sensitivity.
• A beta near zero suggests little measured linear co-movement with the benchmark, and a negative beta suggests opposite co-movement.
• The example uses monthly returns and reports a beta of about 1.09.
• Beta describes relative market exposure and does not ensure a fixed response to future market moves.

Tags

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.