Prime ministers unchained? Explaining prime minister policy autonomy in coalition governments

The personalization of politics has become a central concern in political science. This is also true for parliamentary governments, where the Prime Minister has allegedly acquired an increasing relevance. Nonetheless, a key question remains unanswered: How can we estimate the Prime Minister Policy Autonomy (PMPA) in parliamentary governments? Moreover, what are the determinants of this autonomy? This article aims to answer these questions by proposing a novel and easily replicable index of PMPA, based on data from an analysis of Prime Ministers' and members of Parliament's parliamentary speeches, and specifically from cosine similarity analysis. In this article, we explore PMPA by focussing on two most different cases of coalition governments, Italy and Germany between 1994 and 2014. A multilevel regression analysis shows that coalition-related factors strongly influence PMPA, party-related factors are somewhat relevant, and the Prime Minister-related factor (its selectorate) does not have a significant impact on such autonomy.