The Norwegian economy is an example of a mixed economy; a prosperous capitalist welfare state it features a combination of free market activity and large state ownership in certain key sectors, influenced by both liberal governments from the late 19th century and later by social democratic governments in the postwar era. Public health care in Norway is free (after an annual charge of around 2000 kroner for those over 16), and parents have 46 weeks paid parental leave. The state income derived from natural resources includes a significant contribution from petroleum production. Norway has an unemployment rate of 4.8%, with 68% of the population aged 15–74 employed. People in the labour force are either employed or looking for work. 9.5% of the population aged 18–66 receive a disability pension and 30% of the labour force are employed by the government, the highest in the OECD. The hourly productivity levels, as well as average hourly wages in Norway, are among the highest in the world.