You just don't know how much. A close race with both candidates in the mid-40 percent range. Every polling agency has its own, closely-held methods for figuring out who's a likely voter, said Newport, and that tweaks the results a bit. Methodology and timing also matter, said Doug Schwartz, director of polling at Quinnipiac University in Connecticut. A debate or campaign visit right before a poll can alter results.
Pollsters can also, if they choose, slant their polls.
The number of people called also affects a poll. A sample of about 1,000 people creates a 3-point margin of error, Schwartz said. But you can't get rid of the margin entirely, which is what puts the art into polling. ABC News Internet Ventures. Click here for Terms of Use and Privacy Policy and Internet Safety Information applicable to this site.