How voter ID polling weight distorts poll results...

President Obama approve/disapprove numbers for April 5, 2009...

CBS/NYT shows a 66% approval, 24% disapproval (+42) using a voter ID polling weight of 39D, 23R, 38I (Democrats +16)
Rasmussen shows 58% approval, 41% disapproval (+17) using a voter ID polling weight of 39D, 33R, 28I (Democrats +6)
Exit polling taken on election day Tuesday November 4, 2008 shows a voter ID party affiliation of 39D, 32R, 29I (Democrats +7)

CBS/NYT used 9% less Republicans in their polling data than voted on election day.
Rasmussen used 1% more Republicans in their polling data.
The result was an 8% difference in appoval & a 25 point difference in the spread...