Module 2: Pricing Risk - CAPM and The Security Market Line
If MPT builds the portfolio, the Capital Asset Pricing Model (CAPM) prices the specific assets within it. Developed by William Sharpe, CAPM provides a formula to calculate exactly what return an investor must demand to justify the risk of buying a specific US stock.
1. The CAPM Formula
E(Ri) = Rf + Ξ²i x [E(Rm) - Rf]
- E(Ri): The Expected Return of the specific stock.
- Rf (Risk-Free Rate): The yield on a 10-Year US Treasury bond. The absolute baseline return required to defer consumption.
- Ξ²i (Beta): The measure of the stock's volatility relative to the S&P 500. A Beta of 1.5 means the stock is 50% more volatile than the market.
- [E(Rm) - Rf] (Equity Risk Premium): The extra return the aggregate US stock market generates above the risk-free rate to compensate investors for taking on equity risk.
2. The Security Market Line (SML)
The SML is the graphical representation of CAPM. It plots Expected Return against Beta. If a stockβs expected return plots above the SML, it is undervalued (offering excess return for its risk). If it plots below the SML, it is overvalued.
Case Study: The Beta Distortion in Tech
During the late 2010s, US software companies possessed massive Betas (e.g., 2.0).
- Analysis: Under CAPM, a Beta of 2.0 mathematically requires a massive Expected Return. Consequently, when Wall Street analysts calculated the Weighted Average Cost of Capital (WACC) for these tech firms, the high CAPM output forced them to use aggressive discount rates. This explains why high-Beta growth stocks are so violently sensitive to Federal Reserve interest rate hikes (the Risk-Free Rate component of the equation).
Self-Assessment Quiz
- Break down the components of the "Equity Risk Premium" within the CAPM formula.
- If a stock possesses a Beta of 0.5, will its Required Return be higher or lower than the overall S&P 500?