Foreclosed homes permeate the American landscape. According to data from the Massachusetts Institute of Technology (MIT), they make up about one in 12 houses with under $1 million left on the mortgage. These foreclosures drive down home prices, but it can be hard to determine how much depreciation is caused by the foreclosure and how much is economical factors. One economist from MIT and two Harvard researchers have put a price tag on foreclosures. They've determined that foreclosure itself reduces the value of a home by 27 percent.