Modest decreases in home prices and interest rates resulted in a slight increase in nationwide housing affordability in the fourth quarter of 2015, according to the National Association of Home Builders/Wells Fargo Housing Opportunity Index. In all, 63.3 percent of new and existing homes sold in the fourth quarter were affordable to families earning the U.S. median income of $65,800. In the third quarter, 62.2 percent of homes sold were affordable to median-income earners, according to a release. The national median home price dropped to $226,000 from $231,000 in the third quarter. Average mortgage rates edged lower to 4.09 percent from 4.18 percent in the same period.