With trends that seem counter-intuitive, predicting the take-up of private health insurance can be tricky. People with private insurance are less likely to be in poor health and have fewer long-term health conditions than those who rely on the public system. But there are methods for modelling choice behaviours and policy-makers would do well to employ them, argues Michael Keane, an economics professor at the Australian School of Business. Attempts to control hospital waiting times through the private health insurance market are unlikely to be successful. Insurance take-up seems driven by the mixed motives of risk aversion, cognitive ability and income.