Foundations of Portfolio Theory

Prize Lecture to the memory of Alfred Nobel, December 7, 1990.Portfolio Theory;

Risk and Lack of Diversification under Employee Ownership and Shared Capitalism

Some analysts view risk as the Achilles Heel of employee ownership and to some extent variable pay plans such as profit sharing and gainsharing. Workers in such "shared capitalist" firms may invest too much of their wealth in the firm, contrary to the principle of diversification. This paper addresses whether the risk in shared capitalism makes it unwise for most workers or whether the risk can be managed to limit much of the loss of utility from holding the extra risk. We create an index of financial security based on worker pay and wealth, and find that workers who feel financially insecure exhibit fewer of the positive outcomes associated with shared capitalism, and are less interested than other workers in receiving more employee ownership or even more profit sharing in their workplaces. This response is substantially lessened, however, when accounting for worker empowerment, good employee relations, and high-performance work bundles that appear to buffer worker response toward risk and increase interest in shared capitalism plans. We also discuss portfolio theory which suggests that any risky investment -- including stock in one's company -- can be part of an efficient portfolio as long as the overall portfolio is properly diversified. We show that given estimates of risk aversion parameters, workers could prudently hold reasonable proportions of their assets in employee stock ownership of their firm with only a modest loss in utility due to risk. A good strategy for firms is to personalize individual portfolios on the basis of worker characteristics and preferences, developing investment strategies that would diversify each worker's entire portfolio in ways consistent with individual risk preferences.

Searching for the Kuhnian moment : the Black-Scholes-Merton formula and the evolution of modern finance theory

The Black-Scholes-Merton formula has been put to widespread use by options traders because it provides a means of calculating the theoretically 'correct' price of stock options. Traders can therefore see whether the market price of stock options undervalues or overvalues them compared with their hypothetical Black-Scholes-Merton price, before choosing to buy or sell options accordingly. As a consequence of this close relationship between options pricing theory and options pricing practice, a strong performativity loop was activated, whereby market prices quickly converged on the hypothetical Black-Scholes-Merton prices following the dissemination of the formula. The theory has therefore had significant real-world effects, but how should we characterize the initial instinct to derive the theory from a philosophy of science perspective? The two books under review suggest that a Kuhnian reading of the advancement of scientific knowledge might well be the most appropriate. But, on closer inspection, it becomes clear that the publication of the Black-Scholes-Merton formula should not be seen as a Kuhnian moment with paradigm-shaping attributes. It is shown that, at most, the formula acts as an important exemplar which, via its use in the training of options pricing theorists and options pricing practitioners, reinforces the entrenchment of finance theory within the orthodox economics worldview