Inflation occurs when governments create and circulate more money than needed by their nations' economies. This causes the purchasing power of money to shrink and prices to increase. Media outlets often use the Consumer Price Index (CPI) as the sole measure of inflation, but another type of inflation also occurs when governments create more money than required by their economies. This is called "asset inflation," and it raises the prices of assets like stocks, real estate, and commodities. This phenomenon increases the wealth of those who already own assets, while making those assets less affordable for people with little wealth. One way to measure asset inflation is to compare a country's net wealth to the size of its economy. Since 2009, this measure has increased by 48% in the United States. A primary driver of asset inflation and consumer price inflation has been the Federal Reserve creating $8.9 trillion in new money to pay for rising government spending on social programs.