I've given this advice an number of times now. But this is such an interesting example it seemed appropriate to mention it again.
One of the biggest ways to detect biased polling is to watch the actions of the candidates. If polls suggest a state is definitely going one way or the other, yet both candidates continue to dump resources in to the state, you can be sure that their internal numbers say the state is close. Remember, most polling companies are paid to do their polling and as such, they bend their results to make the person footing the bill happy. The internal polling that a campaign pays for is specifically directed to be more accurate and less biased. We never see those numbers publicly as both sides are trying to influence your behavior and enthusiasm with biased polling.
Today McCain appeared in Iowa and is opening up more offices there. This is somewhat surprising. Check that, this is very surprising as national polling suggests that Iowa is going to go heavily towards Obama. The Real Clear Politics spread has Obama +11.8 in Iowa.
The explanation as to why the traditionally red Iowa is blue this year is simple--corn subsidies. Obama supports corn subsidies, McCain does not. Given how much corn Iowa produces this is enough to push Iowa in his favor. Or so the common wisdom says.
But if that is true, why is McCain in Iowa? Why is his campaign opening offices there? They must have internal numbers that suggest something far different than the public polls.
Just how far off is public opinion polling this year?