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

We consider investors with mean-variance-skewness preferences who aim at selecting oneout of F different funds and combining it optimally with the riskless asset and direct stock holdings.Direct stock holdings are either exogenously or endogenously determined. In our theoretical section,we...

We develop a model of portfolio choice capable of nesting the views of Keynes, advocating concentration in a few familiar assets, and Markowitz, advocating diversification across all available assets. In the model, the return distributions of risky assets are ambiguous, and investors are averse...