A panel of FICO economists recently projected that the U.S. housing market will face recession-era struggles through the rest of the decade. As if that report were not evidence enough of the sector's woes, new research may provide some reasoning: equity, or lack thereof. Analytics firm CoreLogic reported this week that 10.7 million - or 22.1 percent - of all residential properties with a mortgage held negative equity at the end of the third quarter. While the figure remains high, it is lower than the 22.5 percent noted during the second quarter. Defined as the tricky situation in which borrowers owe more on their mortgages than their homes are worth, negative equity may be caused by a decline in property value, a hike in mortgage debt or both. Whatever the cause, the trend continues to mire the housing sector, and, coupled with foreclosure rates, one can begin to grasp why analysts do not foresee a recovery any time soon. "Although slightly down, negative equity remains very high and renders many borrowers vulnerable when negative economic shocks occur, such as job loss or illness," said Mark Fleming, chief economist at CoreLogic. "[Mortgage debt] overhang is holding back the recovery of the housing market and broader economy."