How much did central bank mortgage bond purchases narrow mortgage spreads?
Core argument: The actual mortgage spread fell 113 bps from early 2020 to 2021, and the authors estimate that without Fed MBS purchases it would have declined only 75 bps, implying Fed purchases compressed the spread by 38 bps.
Banks and the Fed are the largest providers of mortgage credit in the economy. The Fed’s supply of mortgage credit consists of buying or selling mortgage-backed securities (MBS) under its quantitative easing and tightening (QE and QT) programs. Banks’ supply of mortgage credit is driven by the deposits channel of monetary policy: banks increase mortgage credit when the Fed lowers interest rates and contract it when the Fed raises them. Panel B of Figure 23 plots the actual mortgage spread against counterfactual mortgage spreads without Fed purchases and without Fed and bank purchases. We obtain the counterfactual spreads by adding the estimated impact [which depends on the sum of instrumental variables estimates of the two demand elasticities] back into the actual spread. The actual mortgage spread drops sharply by 113 bps from early 2020 to 2021. We estimate that if the Fed had not purchased MBS, the spread would have declined by 75 bps over this period. This implies that Fed purchases contracted the mortgage spread by 38 bps. If we also take away bank MBS purchases, the mortgage spread declines by just 32 bps and remains relatively flat during the period.



