When aggregating portfolio metrics, why is diversification and correlation considered?

• A. They are not important in real estate modeling.
• B. They ensure the portfolio IRR equals the weighted average of individual IRRs.
• C. They help capture risk reduction from diversification and inter-property correlations, improving portfolio risk estimates.
• D. They simplify the model by assuming all properties behave identically.

Answer: (C)

Diversification and correlation matter because portfolio risk isn’t simply the sum of each property's risk. When you combine properties, their returns move together to different extents. Diversification lowers overall risk by mixing assets whose cash flows aren’t perfectly correlated, so weak or negative moves in one property can be offset by better performance in another. Correlation provides the quantitative link—how similarly different properties respond to market forces. In real estate, factors like occupancy, rents, cap rates, and financing costs are driven by macro and local conditions, so some properties will track each other closely while others don’t. By accounting for these relationships in the portfolio (through variances and covariances), you get a more accurate estimate of portfolio risk, which informs better capital allocation and risk management. If you assumed all properties behave the same or are perfectly correlated, diversification benefits vanish and risk would be misrepresented.