Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
The performance of parties at the national level is likely to influence election results at the local level, and vice versa. However, researchers have not yet quantified those electoral externalities. We apply vector autoregressions with predetermined variables to new high‐frequency opinion poll data for the German state of Berlin, measuring voting intentions of Berlin voters for the state parliament and for the national parliament. Our results show that the impact of local politics on national elections has been drastically underestimated so far. Shocks in state parliament voting intentions influence national parliament voting intentions to the very same extent as vice versa. Externalities account for around 10% to 40% of the variation at the other level of government. Left‐wing parties interact somewhat more strongly between different levels of government than right‐wing parties, and effects are more persistent.