Explanation

Jensen's alpha is most appropriate when measuring portfolio performance for well-diversified portfolios where diversifiable risk (idiosyncratic risk) is negligible. Here's why:

Key Concepts:

1. Jensen's Alpha measures the excess return of a portfolio relative to its expected return based on the Capital Asset Pricing Model (CAPM).
2. CAPM Assumptions: The model assumes investors hold well-diversified portfolios, eliminating idiosyncratic (unsystematic) risk.
3. Diversifiable vs. Non-diversifiable Risk:
   • Idiosyncratic risk: Risk specific to individual assets that can be eliminated through diversification
   • Systematic risk: Market risk that cannot be diversified away

Why Option C is Correct:

• When an investor holds a well-diversified portfolio, the only relevant risk is systematic risk (beta).
• Jensen's alpha uses CAPM, which assumes perfect diversification, making it appropriate for evaluating such portfolios.
• The alpha represents the manager's skill in generating returns beyond what would be expected given the portfolio's systematic risk.

Why Other Options are Incorrect:

• Option A: Jensen's alpha is NOT appropriate when idiosyncratic risk is relevant because CAPM assumes this risk has been eliminated through diversification.
• Option B: Jensen's alpha is not specifically designed for comparing different asset classes like real estate vs. equity; it's better suited for comparing portfolios within the same asset class framework.

Practical Application:

Jensen's alpha is widely used to evaluate mutual fund and portfolio manager performance, particularly for equity portfolios that should be well-diversified according to modern portfolio theory principles.