evidence: The same is true of other sources of non-sampling error. The group of people pollsters can reach by using live telephone interviewers may have different voting intentions than those they can reach by automated phone calls, or via the internet. Individual pollsters may make methodological choices, such as weighting schemes, that consistently lead to more or less favourable results for a particular political party. [...] Putting the pieces together [...] Like all models, our forecast relies on the assumption that the historical relationships that have governed voter behaviour and pollster accuracy in the past will continue into the future. In politics, unlike physics, this is not guaranteed. Sooner or later, voters will do something that past precedents implied was exceedingly unlikely, and models like ours will be subjected to a fresh round of criticism. But as long as such "black-swan" events happen roughly as much as we expect them to—neither too often nor too infrequently—our model will be doing its job. And if our stated probabilities do wind up diverging from the results, we welcome the opportunity to learn from our mistakes and do better next time.■