Kayser, Leininger model sees possible grand coalition or CDU/FDP/Greens.

Berlin, 15 June 2017 –The CDU/CSU will gain 35.1 percent of the vote and be the strongest party in the 2017 Bundestag election, but will lose a good six percent compared to 2013, according to a scientific forecast by Mark Kayser and Arndt Leininger of the Hertie School. The SPD will improve only slightly, garnering 26.1 percent of the vote. The Greens should expect 10.5 percent, which is better than their current showing in polls and implies that they are underperforming in their electoral potential. The Left Party (Die Linke) should take 9.2 percent of the vote, and the FDP will return to parliament with 8.7 percent of the vote. The AfD is expected to gain 7-9 percent of the vote. This could mean either a continuation of the grand coalition led by the CDU/CSU, or a coalition of CDU/CSU, the Greens and the FDP.

Kayser and Leininger developed a so-called structural forecasting model to obtain the results. As opposed to polling, forecasting models use large volumes of historical data to make predictions. The model is based not only on the most recent German state parliament election results, but also takes into account state and federal elections going back to 1961, weighting state elections that are held close to national elections more heavily. Calculations are aggregated into a final forecast, taking into account, among other things, differences in voter turnout.

The predictions are based on the actual electoral behaviour of citizens, as opposed to surveys, which show hypothetical behaviour. This makes it possible to compile realistic expectations before the election. “We predict how average candidates would perform in average campaigns. On the evening of 24 September, we can see which parties have effectively campaigned and successfully mobilised their electoral potential and which have not,” explain Kayser and Leininger.

Mark Kayser is Professor of Applied Methods and Comparative Politics at the Hertie School. Arndt Leininger has just completed his doctorate at the Hertie School and is now a research associate at the University of Mainz.

A longer version of this article has just been published on Cambridge Core in PS: Political Science & Politics, Volume 50 / Issue 3 and is available here (in English).