For the CAPM to be useful, a portfolio must have the following
characteristics:
- The portfolio must be fully diversified and there is no
firm-specific risk in the portfolio
- The portfolio must have only the market risk
- The risk-free asset in the portfolio can be bought and sold at
the risk-free rate
- There are no transaction costs associated with buying and
selling the stocks within the portfolio
- Any number of stocks can be bought and sold at the market
price