How do voters' assign responsibility for government outcomes in coalition governments? The ability of voters to assign responsibility for outcomes is of high relevance for the democratic function of parliamentary elections but remains poorly understood. According to existing observational studies voters rely heavily on a party's control over the office of prime minister, as an informational shortcut to identify the agenda-setter within a coalition government, and assign responsibility. Yet, there exists little theory and evidence on the effect of institutional prime ministerial powers and their usage on the role of prime ministers as informational shortcut for voters. This manuscript lays out a research design to causally identify responsibility assignment among coalition parties under different prime ministerial power contexts. It employs a vignette experiment in varying contexts of prime ministerial powers and makes use of a scheduled transition of the office of prime minister between coalition parties as a natural experiment. The results of this study have important implications for our understanding of how prime ministerial behaviour and powers can affect electoral accountability in coalition governments.