Replication Data for: Coalition Inclusion Probabilities: A Party-Strategic Measure for Predicting Policy and Politics

What predicts policy outcomes in coalition governments? The most successful policy making models assume unitary, single party government while a second approach using measures of electoral competitiveness has also had limited success predicting policy outcomes from multiparty governments. We argue that previous efforts to predict policy in coalition governments neglect (a) that outcomes depend on negotiations between parties and (b) that policy-making continues between elections. We conceptualize, estimate and validate a novel dynamic measure of parties’ bargaining leverage intended to predict policy and politics in coalition governments. Combining a large set of political polls and an empirical coalition formation model developed with out-of-sample testing, we estimate a new measure of bargaining leverage – each party’s probability of inclusion in an alternative coalition if one were to form – in a sample of 21 parliamentary democracies at a monthly frequency over four decades. Applications to government spending and to the stringency of environmental policy show coalition leverage to be strongly predictive while the non-bargaining alternative, vote intention polls, is not.