Coalition inclusion probabilities: a party-strategic measure for predicting policy and politics

Abstract

Policy in coalition governments (a) depends on negotiations between parties that (b) continue between elections. No extant means of predicting policy—bargaining power indices, vote shares, seat shares, polling, veto players or measures of electoral competitiveness—recognizes both of these facts. We conceptualize, estimate and validate the first dynamic measure of parties’ bargaining leverage intended to predict policy and politics. We argue that those parties with the greatest leverage in policy negotiations are those with the highest probability of participating in an alternative government, were one to form. Combining a large set of political polls and an empirical coalition formation model developed with out-of-sample testing, we estimate coalition inclusion probabilities for parties 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 leverage from coalition inclusion probabilities to be strongly predictive while the primary alternatives—vote shares, seat shares and polls—are not.

Now You See Me, Now You Don't: Anticipatory Coalitional Strategies in European Representative Democracies

“…7 The MARPOR project uses quasi-sentences as its minimal unit, and the proportion is measured as the number of quasi-sentences devoted to a specific policy category out of all quasi-sentences with policy content. 8 Compared to Kayser et al (2022), I measure the potential cabinet's preference range in two dimensions and rely on seat figures rather than polling figures. I also estimate two separate models for the CHES data subset and the MARPOR data subsets.…”

“…Mark Kayser et al (2022) have developed what they term a measure of coalition inclusion probability, or CIP. Building on earlier models of government formation, most notably Lanny Martin and Randolph Stevenson (2001, 2010), they estimate a conditional logit model predicting the likeliest governments to form.…”

“…While one component of a party's likelihood of being a member of a coalition is its choice of strategy, it is not the only one. The ideological character of a potential cabinet contributes to its likelihood of being formed as well (Kayser et al 2022; Martin and Stevenson 2001, 2010). It would therefore be reasonable that a potential cabinet's ideological position is also of relevance to the choice of strategy by its potential members.…”

“…8Compared to Kayser et al (2022), I measure the potential cabinet's preference range in two dimensions and rely on seat figures rather than polling figures. I also estimate two separate models for the CHES data subset and the MARPOR data subsets.…”

“…Primarily, adjusting salience applies to parties in a position of intermediate bargaining strength – here operationalized as their coalition inclusion probability (Kayser et al 2022) – that is, parties that are likely to be a member of some government coalition, but not overwhelmingly so. To test if parties adjust the salience of issues that are less important to them, I estimate a dynamic model (system generalized method of moment, GMM) on a panel of parties from post-electoral formation opportunities in up to 27 European parliamentary and semi-presidential democracies between 1970 and 2019 2 .…”