The thee-factor model captures variations in asset returns that the CAMP misses. Behavioralists argue that violations of the CAPM reflect irrational pricing that the three-factor model catches with the B/M factor. In fact, it is impossible to tell whether the problem in explaining returns in because of irrational pricing or rational pricing in an incomplete mode. Testing the CAPM is difficult because of lack of theoretical or empirical clarity on what constitutes the market portfolio. Some argue that it is impossible to test the CAPM because empirical results test whether the market portfolio proxy is efficient but tell nothing about the CAPM. Efforts to find a reasonably efficient proxy have extended the market portfolio to include assets other than stocks and international assets. Still, the market proxy is ineffective because adding the B/M and other variables in regressions effectively annuls the CAPM-predicted beta-expected return relationship.