Who gets what and when in coalition governments? The party with the credible exit threat, shows research by Mark Kayser and Jochen Rehmert

In Political Science Research and Methods, the researchers explore coalition bargaining leverage.

What motivates coalition governments to switch policy positions? New research by Mark Kayser, Professor of Applied Quantitative Methods and Comparative Politics at the Hertie School, Matthias Orlowski, a data scientist at Neuraum Ventures in Berlin, and Jochen Rehmert of the University of Zurich demonstrates that shifts in polling and public opinion rarely change the policy of an existing government. But they found one important exception: cases in which shifts in polling change the probability of a coalition member being able to leave the current government for an alternative one if new elections were to be held.

“This has large consequences for the responsiveness of coalition governments in parliamentary democracies,” says Kayser. But how does one know when a credible exit threat can be made? The co-authors calculate the monthly probability of each party being included in a new government for nearly all parties in 21 democracies. Most changes in polling do not make new coalition geometries possible, but when they do, policy is most likely to change in favour of the party with the new exit option.

The open access paper, “Coalition inclusion probabilities: a party-strategic measure for predicting policy and politics,” appeared online in January in Political Science Research and Methods, a publication of Cambridge University Press. The authors aim to offer a systematic means to predict policy outcomes in coalition governments.

In parliamentary democracies, there are always credible threats that smaller parties might leave the coalition, Kayser says. This credible threat can help parties when negotiating with fellow members of government. “If you're a party in government, and you could easily leave that government to join an alternative government, then you've got a lot of power.”

For every party in a large set of 21 parliamentary democracies, Kayser and his fellow researchers have calculated the probability of whether the party would be included in government if an election were held that month – with data going back decades. Via the small monthly shifts in poll percentages, they can determine the points at which a coalition member could threaten to leave the government and form another ruling coalition, and this is the point at which a “credible threat” turns into bargaining power over policy choices.

“So we can ask in any month historically, what's the probability of each party being in an alternative government? What is their leverage? How much negotiating power do they have?” Kayser says. “The idea was to create a measure, and then in a next step to predict policy change.”

The current paper follows a first paper predicting changes in environmental policy stringency. The paper published online in Legislative Studies Quarterly in 2020 showed that such a shift took place in Germany just as the government decided to exit nuclear power after the Fukushima nuclear accident in 2011. A shift in polling eroded the coalition relevance of a smaller governing party, the Free Democrats, as polling for the opposition Greens made them a viable potential coalition partner for Angela Merkel’s Christian Democrats. The Free Democrats’ lack of credible alternative coalition options left them too weak to stop their coalition partner from courting the Greens by accelerating the German nuclear phase-out, Kayser says. Shifts in polling only matter for policy outcomes when they change coalition options.

Find the paper in Political Science Research and Methods here.


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More about our expert

  • Mark Kayser, Professor of Applied Methods and Comparative Politics