A likely voter is someone who is registered to vote in an upcoming election and is deemed likely to vote in that election, for example, by pollsters trying to forecast the election outcome. Pre-election pollsters face a unique challenge. At their most germane, they seek to sample a population that is unknown and indeed technically unknowable, because it does not and will not exist until on and around Election Day; this population is the voting public. For a survey that seeks to measure the attitudes and intentions of voters in a given election, the only recourse is to estimate this population through a process known as likely voter modeling.

There are no fixed rules for likely voter modeling, and techniques vary. But all begin with a ...