The CAPM is based on the assumption that investors hold a combination of the market portfolio and risk-free assets. Furthermore, it assumes that the set of means, volatilities, and correlations are the same for all investors, i.e., the investors have homogeneous expectations. In addition, the market is at equilibrium, where demand is equal to supply. It also assumes investors do not hold concentrated portfolios. Rather, they hold well-diversified portfolios that eliminate specific risks.

Things to Remember

The Capital Asset Pricing Model (CAPM) is a financial model that is used to determine the expected return on an investment given its risk. It is based on several assumptions, including the assumption that investors have homogeneous expectations, that the market is in equilibrium, and that investors hold diversified portfolios. These assumptions are necessary to simplify the model and make it applicable to a wide range of scenarios. However, in reality, these assumptions may not always hold true. For example, investors may have different expectations based on their individual circumstances, markets may not always be in equilibrium due to various factors, and many investors may not hold diversified portfolios due to various reasons. Therefore, while the CAPM is a useful tool for estimating the expected return on an investment, it is important to understand its limitations and use it in conjunction with other financial models and tools.