http://usconservatives.about.com/b/2012/05/03/3-new-swing-state-polls-show-bad-news-for-obama.htmFlorida:
The poll shows Romney leads Obama by 44-43%, after figures are weighted. (In weighting, pollsters can alter the data to reflect what they believe the actual election turnout will be, so as to minimize the effect of skewed polling samples. This estimate can be quite subjective). Before weighting, Romney's lead was larger. So, how did the pollster weight the Florida data? The Republican sample was weighted to be only 28% despite being 36% in 2010 (a "Republican year") and 34% in 2008 (a "Democrat year").
The weighting also reflects the pollsters opinion that Democrat turnout will be 3% higher than Republican turnout, 3% points higher than it was in 2010 and equal to 2008. So even by weighting to Democrat-favorable 2008 turnout figures (unlikely to be repeated in 2012), Obama is still trailing.
Ohio:
In Ohio, it's more of the same, but even a lot worse. While the poll shows Obama winning by just 44-42%, those figures also reflect very favorable Obama assumptions. Once again, the polling sample is weighted to drop Republican turnout to a shockingly low 24% while it was 37% in 2010 and 31% in 2008. Meanwhile, the pollster kept Democrat turnout at 36%, exactly where it was in 2010 and only 3 points less than 2010.
So while turnout in 2010 saw Republicans at 37% to 36% for Democrats, this poll "weights" the turnout to be 36% for Democrats and 24% for Republicans. And even then, Obama's lead is just 2%. If you weight the Ohio numbers to actual 2010 turnout, Romney leads 48-42%. So, a lot of these polls reflect only how pollsters prefer to "weight them." But in any case, a weighted sample of 24% for Republicans is extremely low.
Pennsylvania
Pennsylvania is much of the same. While Republicans made up 37% of the electorate in both 2008 and 2010, the pollster once again weights the information so that Republican turnout is just 29%. The Democrat have a 7 point margin advantage in the weighted sample, equal to 2008 (and more than double the 3 point advantage of 2010). Here, Obama is still at only 47%, even though he scored 55% of the PA vote in 2008 (and even though a large chunk of the GOP has apparently moved out of the state according to the pollster).