As a portfolio manager, you are evaluating different commodity indices for potential inclusion in a diversified investment strategy. You are particularly interested in how these indices capture price movements across various commodities and their implications for portfolio performance. Your research includes looking into the various methodologies used to construct these indices, as well as how rolling contracts in futures markets might impact returns over time.
Considering the rolling yield in commodity indices, which of the following statements correctly addresses the impact of contango and backwardation on a commodity index portfolio?