The trade-off between growth and risk in Kelly’s gambling and beyond

We study a generalization of Kelly’s horse model to situations where gambling on horses other than the winning horse does not lead to a complete loss of the investment. In such cases, the odds matrix is non-diagonal, which is particularly interesting for biological applications. We examine the trade-off between the mean growth rate and its asymptotic variance, an approximation for risk. Because the consequences of fluctuations around the average growth rate are asymmetric, we further explore a better alternative definition of risk: the extinction probability and its implications for Kelly gambling and the risk-return trade-off. We discuss some applications of these concepts in biology and ecology.