Forecasting the 2013 Bundestag Election Using Data from Various Polls

CDU/CSU 38.1%, SPD 28.2%, B‘90/Die Grünen 13.5%, Die Linke 7.7%, FDP 5.4%, others 6.5% – these are our (point) estimates of the party vote shares at the upcoming Bundestag election. In contrast to the predominant academic approach to forecast incumbent vote shares from measures of government popularity, economic conditions and other fundamental variables (Jérôme, et al. 2013, Kayser and Leininger 2013, Norpoth and Gschwend 2013), we entirely rely on data from published trial heat polls. Opposite to common practice in the news media, we do not take isolated polls as election forecasts in their own right. Instead, we use historical data to empirically assess the relationship between polls and election outcomes, and combine extrapolations from 42 current polls in a Bayesian manner. A retrospective evaluation of our method compared against other approaches will be given after the election on September 22