If the rate of return on the S&P 500 index was 23% for 2009, and the risk-free rate at the end of 2009 was 1%, calculate the equity risk premium for 2009? Recalculate the equity risk premium using 1981 data, when the risk free rate was 15% and the S&P 500 index return was minus 10%. What are the implications of different equity risk premia numbers for different time periods? HINT: When you use the CAPM, you must enter an equity risk premium. Therefore, how do you do that accurately when data for different years produce different equity risk premia?
I am under the impression that we cannot calculate this because beta requires the rate of return on a single asset in the market and this was not provided. Is that right or am I missing something?