A new study by Federal Reserve Board economists concludes that the large retained portfolios of Fannie Mae and Freddie Mac “have essentially no short- or long-term effects on either primary or secondary market spreads.” The researchers – Andreas Lehnert, Wayne Passmore and Shane Sherlund – looked at monthly purchase activity by the government-sponsored enterprises and mortgage origination estimates by Inside Mortgage Finance, an affiliated newsletter. They reported finding evidence that GSE portfolios tend to rise when...