The German election has two faces. Most observers consider the race at the top over, with conservative Chancellor Angela Merkel running around 15 percent ahead of her Social Democratic (SPD) rival Martin Schulz. Yet skepticism remains about the accuracy of pre-election opinion surveys. After all, the overwhelming majority of pollsters failed to predict victories for the pro-Brexit camp in the UK and Donald Trump in the US. The methodologies used by German pollsters range from the telephone interviews employed by established organizations like Infratest dimap and Forsa, which have standing contracts with major news outlets, and online surveys used by...