This conclusion is based on the difference between the average earnings of two otherwise-identical individuals with different levels of education. In other words, it measures the expected return to investment in human capital. However, investment should be evaluated taking into account both risk and return. Trade-offs between risk and return play a central role in standard financial and economic models of investment in physical capital. Think about the role of risk in financial investment for a moment – everything else being equal, a risk-averse agent would prefer a less risky portfolio. Because most human beings are risk-averse, we would attach a higher value to a low-risk portfolio than a high-risk one, even if the two portfolios have the same expected returns. Just as financial risk affects the value of an investment portfolio, earnings risks should also affect the value of college education.