Central banks have been using quantitative easing to lower long-term interest rates when short-term rates are stuck at zero. By adding central bank reserves to a model, researchers found that QE programs have reduced long-term yields by 85 basis points. A quarter of this effect is due to increased liquidity, while three-quarters are due to increased supply of reserves. Comparing US and Swiss data shows that the Swiss National Bank's lack of government bond purchases resulted in different effects on the yield curve.