The all too common sunk cost effect is apparent when an investor influenced by what has been spent already persists in a venture, committing further resources or foregoing more profitable opportunities, when the economically rational action is to quit. Less common but arguably just as much a sunk cost effect is the mistake of giving up on a failed or failing venture too readily, sometimes out of nothing but pique at what has been lost, or perhaps through the more subtle (...) psychological forces posited by Kahneman, Tversky, Thaler and others within prospect theory and related work on ``mental budgeting''. Two case examples are considered, wherein decision makers dissatisfied with the results of their investments, and having lost money, appear to compound their losses by selling out at prices less than their own estimates of the remaining financial worth of the failed assets. These decisions are evaluated from the perspectives of both behavioral and prescriptive economics, and are found to have possible explanations in both. Their prescriptive rationale assumes a portfolio theory of investment decisions, and is demonstrated within both expected utility (economics) and mean-variance (finance) frameworks. (shrink)

Simulation evidence obtained within a Bayesian model of price-setting in a betting market, where anonymous gamblers queue to bet against a risk-neutral bookmaker, suggests that a gambler who wants to maximize future profits should trade on the advice of the analyst cum probability forecaster who records the best probability score, rather than the highest trading profits, during the preceding observation period. In general, probability scoring rules, specifically the log score and better known “Brier” (quadratic) score, are found to have higher (...) probability of ranking rival analysts in predetermined “correct” order than either (i) the more usual method of counting categorical forecast errors (misclassifications), or (ii) an economic measure of forecasting success, described here as the “Kelly score” and defined as the trading profits accumulated by making log optimal bets (i.e. Kelly betting) against the market maker based on the probability forecasts of the analyst being assessed. This runs counter to the conventional wisdom that financial forecasts are more aptly evaluated in terms of their financial consequences than by an abstract non-monetary measure of statistical accuracy such as the number of misclassifications or a probability score. (shrink)