We show that a well-diversified portfolio of randomly chosen stocks must include at least 30 stocks for a borrowing investor and 40 stocks for a lending investor. This contradicts the widely accepted notion that the benefits of diversification are virtually exhausted when a portfolio contains approximately 10 stocks. We also contrast our result with the levels of diversification found in studies of individuals' portfolios.

When will borrowers choose fixed rate mortgages and when will they prefer index-linked mortgages? Baesel and Biger (BB) [1] proposed a model that answers this question. According to the BB model, a borrower's preference depends on the difference in interest rates between the fixed and index-linked mortgages, and on the covariance between the borrower's labor income and the rate of inflation. The purpose of this note is to propose a more complete model of borrower preferences. The novelty of the model lies in the inclusion of the value of the house (net of mortgage obligation) in the terminal wealth of the borrower. This inclusion leads to differences between this model and the BB model in the identification of the cases where borrowers will prefer fixed or index-linked mortgages.

We develop a positive behavioral portfolio theory (BPT) and explore its implications for portfolio construction and security design. The optimal portfolios of BPT investors resemble combinations of bonds and lottery tickets, consistent with Friedman and Savage's (1948) observation. We compare the BPT efficient frontier with the mean-variance efficient frontier and show that, in general, the two frontiers do not coincide. Optimal BPT portfolios are also different from optimal CAPM portfolios. In particular, the CAPM twofund separation does not hold in BPT. We present BPT in a single mental account version (BPT-SA) and a multiple mental account version (BPT-MA). BPT-SA investors integrate their portfolios into a single mental account, while BPT-MA investors segregate their port? folios into several mental accounts. BPT-MA portfolios resemble layered pyramids, where layers are associated with aspirations. We explore a two-layer portfolio where the low aspiration layer is designed to avoid poverty while the high aspiration layer is designed for a shot at riches.

This paper develops a capital asset pricing theory in a market where noise traders interact with information traders. Noise traders are traders who commit cognitive errors while information traders are free of cognitive errors. The theory includes the determination of the mean-variance efficient frontier, the return on the market portfolio, the term structure, and option prices. The paper derives a necessary and sufficient condition for the existence of price efficiency in the presence of noise traders and analyzes the effects of noise traders on price efficiency, volatility, return anomalies, volume, and noise trader survival.

The well-known tendency of investors to favor cash dividends emerges quite naturally in two new theories of choice behavior [the theory of self-control due to Thaler and Shefrin (1981), and the version of prospect theory set out by Kahneman and Tversky (1979)]. Although our treatment is novel when viewed from the perspective of standard financial theory, it provides explanations for a phenomenon that has long been described as perplexing.

ABSTRACT One of the most significant and unique features in Kahneman and Tversky's approach to choice under uncertainty is aversion to loss realization. This paper is concerned with two aspects of this feature. First, we place this behavior pattern into a wider theoretical framework concerning a general disposition to sell winners too early and hold losers too long. This framework includes other elements, namely mental accounting, regret aversion, self‐control, and tax considerations. Second, we discuss evidence which suggests that tax considerations alone cannot explain the observed patterns of loss and gain realization, and that the patterns are consistent with a combined effect of tax considerations and the three other elements of our framework. We also show that the concentration of loss realizations in December is not consistent with fully rational behavior, but is consistent with our theory.

Why do levels of corporate social performance (CSP) differ so much across countries? We answer this question in an examination of CSP ratings of more than 2600 companies from 36 countries. We find that firm characteristics explain very little of the variations in CSP ratings. In contrast, variations in country factors such as stages of economic development, culture, and institutions account for a significant proportion of variations in CSP ratings across countries. In particular, we find that CSP ratings are high in countries with high income-per-capita, strong civil liberties and political rights, and cultures oriented toward harmony and autonomy. Furthermore, we find that home country factors explain a smaller portion of the overall variations in CSP for multinationals and cross-listed firms than for non-multinationals and pure domestic firms, respectively.