We study the interaction of expansionary rate-based monetary policy and quantitative easing, despite their concurrent implementation, by exploiting heterogeneous banks and the introduction of negative monetary-policy rates in a fragmented euro area. Quantitative easing increases credit supply less, translating into weaker employment growth, when banks’ funding costs do not decrease. Using administrative data from Germany, we uncover that among banks selling their securities, central-bank reserves remain disproportionately with high-deposit banks that are constrained due to sticky customer deposits at the zero lower bound. Affected German banks lend relatively less to firms while increasing their interbank exposure in the euro area.

This paper analyzes the role of common data problems when identifying structural breaks in small samples. Most notably, we survey small sample properties of the most commonly applied endogenous break tests developed by Brown et al. (J R Stat Soc B 37:149–163, 1975) and Zeileis (Stat Pap 45(1):123–131, 2004), Nyblom (J Am Stat Assoc 84(405):223–230, 1989) and Hansen (J Policy Model 14(4):517–533, 1992), and Andrews et al. (J Econ 70(1):9–38, 1996). Power and size properties are derived using Monte Carlo simulations. We find that the Nyblom test is on par with the commonly used F type tests in a small sample in terms of power. While the Nyblom test’s power decreases if the structural break occurs close to the margin of the sample, it proves far more robust to nonnormal distributions of the error term that are found to matter strongly in small samples although being irrelevant asymptotically for all tests that are analyzed in this paper.