Nearly 10 million Americans remain financially trapped by homes worth less than their mortgage debts - an enduring drag on the U.S. economy almost seven years after the housing bust triggered the Great Recession, according to AP. During the first three months of this year, 18.8 percent of homeowners with a mortgage - 9.7 million - owed more on their loans than their properties would sell for, according to online real estate database Zillow. Though that was an improvement from the 25.4 percent figure of a year ago, the share of such "underwater" homeowners is about four times the historic average. An additional 18.1 percent of mortgage holders were "effectively" underwater: They had equity, but the proceeds from selling their home would be too low to recoup the sales costs and also put a down payment on a new property. The consequence is that few Americans are putting their homes on the market, thereby limiting the economic growth made possible by sales. Because of the shortage of homes being listed, bidding wars have inflated prices in parts of the country to levels that squeeze out many first-time and middle class buyers. The problem is most pronounced among starter homes with prices averaging around $100,000, 30.2 percent of whose owners are burdened by underwater mortgages, sometimes called negative equity.