Health spending in OECD countries averages more than 8% of gross domestic product (GDP) and the share is rising. Overall, some three quarters of that spending is publicly financed. Private health insurance accounts, on average, for only a quarter of private-sector financing, although there is great cross-country variation. In a third of the OECD member countries at least 30% of the population has private health insurance, while market size is negligible in nearly as many countries. Private health insurance also plays a variety of roles, ranging from primary coverage for particular population groups to a supporting role for public systems.