The Sharpe-Lintner version assumes a risk-free rate, whereas the Black version of the CAPM allows unlimited short selling. Both imply that beta, the covariance of asset returns with the market relative to variance of the market, is sufficient to explain differences in asset or portfolio expected returns and that the relationship between beta and expected returns is positive. The risk-free rate is the intercept in the Sharpe-Lintner version, but the Black version requires only that the expected market return be greater than the expected return on assets that are uncorrelated with the market.
Early cross-sectional and time-series regression tests on the linear relationship between asset returns and beta show that although the relationship is approximately linear, the observed slope is flatter than the slope predicted by the Sharpe-Linter CAPM. Other early tests find no improvement from additional explanatory variables, indicat-ing that the market proxy portfolio is efficient. This finding is consistent with the Black version.