The paper compares and contrasts the theories and methodologies of financial economics with generalisations drawn from practical experience of institutional investment management. A Dynamic Equilibrium Model is put forward as a much more realistic theoretical framework than the Sharpe Diagonal Model, a downside theory of risk is developed from sports analogies, and a detailed model of human behaviour, incorporating benchmark levels of ‘unintelligent’, ‘intelligent’, ‘optimal’ and ‘rational’ behaviour, is suggested as a replacement for the very restrictive simplifying assumptions of existing theories. On the basis of a classification system derived from parallels with the history of astronomy, it is concluded that, as a scientific framework, the current theories of financial economics are seriously incomplete, the two crucial areas of incompleteness being the absence of a downside theory of risk and the absence of a realistic model of human behaviour under conditions of risk and uncertainty.

An analysis is made of the effect on portfolio performance if assets are continually rebalanced to constant market value proportions, relative to the passive ‘buy and hold’ strategy. The probability that one strategy outperforms the other is evaluated on the basis of a geometric diffusion model of market prices and by reference to historical data.

In this paper a stochastic model office offering UK-style life insurance contracts is used to demonstrate the effect on relative solvency of different investment and bonus strategies. Relative solvency is defined loosely as the probability that an individual insurer does not fall significantly out of line with the rest of the life insurance market, in terms of, for example, asset liability ratios, or payouts to with-profit policyholders. The model uses the Wilkie investment model, extended to incorporate variation between companies in equity performance.