Since the 1979 revolution, government spending has averaged 59% on social policies, 17% on economic matters, 15% on national defense, and 13% on general affairs. Payments averaged 39% on education, health and social security, 20% on other social programs, 3% on agriculture, 16% on water, power and gas, 5% on manufacturing and mining, 12% on roads and transportation and 5% on other economic affairs. Iran's investment reached 27.7% of GDP in 2009. Between 2002 and 2006, inflation fluctuated around 14%. In 2008, around 55% of government revenue came from oil and natural gas revenue, with 31% from taxes and fees. There are virtually millions of people who do not pay taxes in Iran and hence operate outside the formal economy. The budget for year 2012 was $462 billion, 9% less than 2011. The budget is based on an oil price of $85 per barrel. The value of the US dollar is estimated at IRR 12,260 for the same period. According to the head of the Department of Statistics of Iran, if the rules of budgeting were observed the government could save at least 30 to 35% on its expenses. The central bank's interest rate is 21%, and the inflation rate has climbed to 22% in 2012, 10% higher than in 2011. There is little alignment between fiscal and monetary policy. According to the Central Bank of Iran, the gap between the rich and the poor narrowed because of monthly subsidies but the trend could reverse if high inflation persists.