all investors, do not hold highly diversified asset portfolios.
             Practical data measurement problems. There are also practical problems associated with the model such as difficulties with specifying the risk-free rate, measuring beta and measuring the market risk premium.
             One-period time horizon. CAPM assumes investors adopt a one-period time horizon. In practice investors are likely to have differing time horizons and again this would imply varying SML's.
             Single-factor model. CAPM is a single factor model: it relies on the market portfolio to explain security
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