Rate-spread loans accounted for 18.3 percent of all mortgages made in 2007, down from 28.7 percent the previous year, according to data released this week by the Federal Reserve. However, the falling subprime share could be overstated, as a number of subprime lenders that went out of business during the year failed to report data.Rate-spread loans are the Fed’s proxy for subprime as reported...