Of course, the Star-Tribune Newspaper didn't ask everyone in the US who they were going to vote for; instead, they sampled a portion of the total voting population. Since most polls only sample a portion of a larger population, another sample of 1000 people might provide slightly different results. Instead of 55 to 45, another sample might provide 54 to 46. The margin of error is a way to describe this variability.

Cash Fast, a manufacturer of ATM machines, hired a research firm to find out how long it took people to withdraw money. This firm watched 20 people go to an ATM and withdraw money. They kept track of how long each person took and reported an average time of 2 minutes +/- 30 seconds.

So remember the confidence interval = 2 times the margin of error.