The requirement of positive marginal utility only makes it possible to derive a restricted twofund separation theorem for portfolio selection problems replacing the original separation theorem of Cass and Stiglitz (1970). We use our findings for a re-examination of the bias-in-beta problem in...

Investors need performance measures particularly as a means for funds selection in the process of exante portfolio optimization. Unfortunately, there are various performance measures recommended for different decision situations. Since an investor may be uncertain which kind of decision problem...