Political Polls in a Nutshell

The first thing to understand about political polls is that positive polling numbers are useful for political campaigns. They are used both to lend credibility for past performance and, more importantly, to create a sense of momentum and even inevitability. When one side is able to produce overwhelming polling numbers during the campaign, it is able to drastically reduce the enthusiasm for and campaign donations to the opponent's campaign.

Why The Polls Are Screwy (Best to Ignore Them) - Scripsit The Czar of Muscovy

Many folks are not interested in these byzantine and occult weighting systems that are based, ultimately, on desired results. Ever give a kid the answer to a math problem, and then ask him or her to solve the problem knowing the answer? You get handed the right answer, but sometimes some hysterical math to get there. In political science, this is called sophistry. And it is how much of the polling numbers are computed.