Push polls are used in election campaigns, not to gather information about public opinion, but to modify public opinion in favor of a certain candidate, or – more commonly – against a certain candidate. They are called “push” polls because they intend to “push” the people polled towards a certain point of view.
Push polls are not cases of “lying with statistics” as we usually understand them, but it’s appropriate to talk about them since they are very similar to a “lying technique” that I discussed many times, namely leading questions (see here for example). The difference here is that leading questions aren’t used to manipulate poll results, but to manipulate people.
The push poll isn’t really a poll at all, since the purpose isn’t information gathering. Which is why many people don’t like the term and label it oxymoronic. A better term indeed would be advocacy telephone campaigns. A push poll is more like a gossip campaign, a propaganda effort or telemarketing. They’re very similar to political attack ads, in the sense that they intend to smear candidates, often with little basis in facts. Compared to political ads, push polls have the “advantage” that they don’t seem to emanate from the campaign offices of one of the candidates. (Push polls are typically conducted by bogus polling agencies). Hence it’s more difficult for the recipients of the push poll to classify the “information” contained in the push poll as political propaganda. He or she is therefore more likely to believe the information. Which is of course the reason push polls are used. Also, the fact that they are presented as “polls” rather than campaign messages, makes it more likely that people listen, and as they listen more, they internalize the messages better than in the case of outright campaigning (which they often dismiss as propaganda).
Push polls usually, but not necessarily, contain lies or false rumors. They may also be limited to misleading or leading questions. For example, a push poll may ask people: “Do you think that the widespread and persistent rumors about Obama’s Muslim faith, based on his own statements, connections and acquaintances, are true?”. Some push polls may even contain some true but unpleasant facts about a candidate, and then hammer on these facts in order to change the opinions of the people being “polled”.
One infamous example of a push poll was the poll used by Bush against McCain in the Republican primaries of 2000 (insinuating that McCain had an illegitimate black child), or the poll used by McCain (fast learner!) against Obama in 2008 (alleging that Obama had ties with the PLO).
One way to distinguish legitimate polls from push polls is the sample size. The former are usually content with relatively small sample sizes (but not too small), whereas the latter typically want to “reach” as many people as possible. Push polls won’t include demographic questions about the people being polled (gender, age, etc.) since there is no intention to aggregate results, let alone aggregate by type of respondent. Another way to identify push polls is the selection of the target population: normal polls try to reach a random subset of the population; push polls are often targeted at certain types of voters, namely those likely to be swayed by negative campaigning about a certain candidate. Push polls also tend to be quite short compared to regular polls, since the purpose is to reach a maximum number of people.