How political parties change when their voters leave

In the APSA Public Scholarship Program, graduate students in political science produce summaries of new research in the American Political Science Review. This piece, written by Kumar Ramanathan, covers the new article by
Tarik Abou-Chadi, University of Zurich and Lukas F. Stoetzer, Humboldt University of Berlin,
 “How Parties React to Voter Transitions”. 


In the 2017 German federal election, the ruling Union parties (CDU/CSU) lost one million voters to the radical right-wing populist party Alternative for Germany (AfD). As the results were announced, chancellor Angela Merkel promised to address her party’s stark losses: “We want to win voters back from the AfD…We want to offer solutions to their problems by addressing their grievances and fears.” Merkel’s statement suggests that political parties in multi-party democracies shift their ideological positions when their voters abandon them and support rival parties instead. But when do these shifts take place? How can we measure them, beyond anecdotal examples?

Political scientists Tarik Abou-Chadi and Lukas Stoetzer tackle these questions in a new article in the American Political Science Review. They argue that political parties gain useful information after elections take place, including whether they have lost votes and to whom. To find out whether these signals affect parties’ ideological positions, the authors draw on data about voters’ preferences and the content of party platforms from ten Western European countries during the period 1970-2017.

Their analysis shows that parties do change their positions when they lose voters to a rival. However, they only do so when they receive a strong signal that these losses are significantly damaging. For example, in the 2017 German election, Merkel’s center-right party lost 21% of their share of the votes from the previous election while the right-wing populist AfD party nearly tripled its vote share—a stark loss, prompting Merkel to promise changes in her party’s platform. But, parties do not tend to change their positions if they only lose a small number of voters or if they achieve an overall gain despite losing some voters to a rival. The authors’ model estimates that, on average, parties change their ideological positions if they lose more than 5.8% of their share of votes compared to the previous election. “’This innovative study confirms that in multi-party democracies, parties’ platforms can be influenced by the voters who leave them behind.”.

When parties do change, they tend to shift their positions on issues to more closely match the party that poached their supporters. The extent of this ideological shift depends on how many votes they have lost to that competitor. To measure the ideological positions of parties, the authors use the rile scale, which uses the text of party platforms to place each party on a scale from -100 (most left) to 100 (most right). Relatively small differences on the rile scale can indicate significant ideological difference: for example, the ideological distance between the UK Labour and Conservative parties during the 2010 election was 25 points and the distance between the US Democratic and Republican parties during the 2016 election was 44 points. The authors’ model finds that if a party loses 15% of its votes to a competitor, it is likely to shift its ideological positions by about 3.5 points on the rile scale. If the vote loss is 40%, the party shifts is ideology about 8.2 points toward the competitor.

This innovative study confirms that in multi-party democracies, parties’ platforms can be influenced by the voters who leave them behind. As Merkel’s promise after the 2017 German election suggested, it is not always parties that drive political change. Abou-Chadi and Stoetzer remind us that voters can push political parties in new directions too.


  • Kumar Ramanathan is a doctoral candidate in political science at Northwestern University and will be a doctoral fellow at the American Bar Foundation beginning in the fall of 2020. His dissertation investigates how liberal politicians in northern Democratic Party contested and constructed a civil rights legislative agenda during the 1930s-60s, and aims to explain the origins and limitations of racial liberalism as it emerged among these party elites. His research agenda also includes a set of projects on the impact of civil rights law and policy on the politics of social policy after the 1960s, and collaborative projects on immigrant political participation and urban politics. At Northwestern, Kumar is affiliated with the Chicago Democracy Project, the Comparative Historical Social Sciences Working Group, and the Program in Legal Studies. He received his B.A. in political science and philosophy from Tufts University.
  • Article details: American Political Science Review, Volume 114 , Issue 3,  “How Parties React to Voter Transitions”. 
  • About the APSA Public Scholarship Program.