Zweitstimme.org’s forecast in words.

On 22 September 2017, our model projected the following vote estimates for the upcoming German federal elections on 24 September 2017:

CDU/CSU 35.7%, SPD 22.4%, The Left 9.5%, Alliance 90/The Greens 7.8%, FDP 9.3% and AfD 10.8%.

However, as you can see in the election forecast chart above, these values are by no means certain. The bars for each party indicate in what range we expect the actual value to be with an 83% probability. This means that the probability that the actual election outcome will not lie in this range is the same as that of rolling a six with one die—not very likely, but still possible.

What is more decisive is which coalition governments would have a majority in the new Bundestag in absolute terms. Owing to the uncertainty of our forecast, we can only indicate a probability of a certain coalition having an arithmetical majority. It is almost certain that a grand coalition between the CDU/CSU and SPD would have the majority of seats. The probability of a so-called "Jamaica coalition" (black/green/yellow) between the parties of CDU/CSU, Greens and FDP is currently 88%. The corresponding probabilities of other coalition options based on our prediction are indicated above in a graph.

Behind the forecast.

We are a team of electoral researchers from the universities of Mannheim, Zurich and the HU Berlin. Our model combines historical information about German federal elections with current empirical data. Zweitstimme.org will accompany the campaign for the 2017 Bundestag election with scientifically sound forecasts. For feedback on our forecast, please use our contact form or write to feedback@zweitstimme.org.

Zweitstimme.org’s forecast model

The structural component

The structural component of our model is based on factors that have already proved to be relevant for projecting election results in the past (since 1949). These include, for example, the performance of parties in past elections, historical survey data, and information on whether a party provided the Chancellor. In other words, the structural component learns from the regularities of all past federal elections. The early availability of this information (already 200 days ahead of the election) allows an early prediction of the election outcome.

The polling component

However, the structural component alone is often not sufficient to reflect short-term adjustments in the party system or fluctuations in the political climate. We therefore use published values of the so-called Sunday question to take account of an election’s dynamics. In simple terms, to forecast the actual outcomes we combine the information on the regularities of past elections with what we are currently observing in the polls. While the structural component of the model remains stable, our forecast is continuously updated with each newly published poll.

From vote shares to probabilities

Our model uses a so-called MCMC algorithm, which—metaphorically speaking—repeatedly simulates the election outcome; in our case 100,000 times. Based on these simulations, probabilities can then be calculated for all events that are directly related to a party’s predicted vote shares. For example, if the CDU/CSU is ahead of the SPD in approximately 80,000 of the simulations, this corresponds to an estimated probability of 80% that the CDU/CSU will actually perform better than the SPD.

The team behind zweitstimme.org

Prof. Thomas Gschwend, Ph.D

Thomas Gschwend is Professor of Political Science at the University of Mannheim. Numbers and elections determine his main research interests. His research focuses on comparative politics, judicial politics, public opinion, political psychology as well as political methodology.

Motto:
Election forecasts are too serious a matter to be left to public opinion research institutes.

More on his website.

Dr. Simon Munzert

Simon Munzert is a postdoctoral research and teaching fellow at the Chair of Comparative Political Behavior at the Humboldt-Universität zu Berlin. In his doctoral thesis, he studied the measurement of public opinion in subpopulations. Among other things, he investigates election forecasts at local and national level.

Motto:
If you consider a result to be extremely unlikely, your judgement is probably too unlikely.

More on his website.

Dr. Lukas Stoetzer

Lukas Stoetzer is postdoc at the chair of Political Methodology, University of Zurich. His work focuses on the modelling of ideological and strategic choice decisions. A core question of his work is what tendencies and expectations about voters' opinions can be derived from weekly polls.

Motto:
Time x variance: the uncertainty of poll-supported electoral predictions is usually greater than you think.

More on his website.

Sebastian Sternberg, M.A.

Sebastian Sternberg is a Ph.D. student at the Chair of Quantitative Methods in the Social Sciences at the University of Mannheim. While his work concentrates mainly on explaining and predicting the outcome of court decisions, he is enthusiastic about all kinds of predictions, including elections.

Motto:
In theory, theory and practice are the same. In practice, they are not.

Marcel Neunhoeffer, M.A.

Marcel Neunhoeffer is a Ph.D. student at the GESS of the University of Mannheim and a research assistant at the Chair of Quantitative Methods in the Social Sciences. He is particularly interested in the influence of election campaigns on public opinion and election results. In his research, he employs mainly (field) experiments as an investigation method.

Motto:
Good predictions are only ever recognized after the fact.