Polling and the Cell Phone Factor

Brian Schaffner of Pollster.com examines one possibility of why we're seeing disparity between different national polls. Perhaps the difference lies in the cell phone factor.

One can get lost in the deluge of polls which, just this week, show anything from a narrow 1% Obama lead (AP-Gfk) to a substantial margin of 14% (Pew). One pattern that seems to have become particularly evident this week is that the polls showing the biggest leads for Obama tend to be those that are polling the cell phone only population (such as Pew, CBS/New York Times, and ABC/Washington Post). We know from the recent Pew report that excluding cell phone only respondents from the sampling frame reduces Obama's margin by 2-3%, even when the sample is weighted. But how does this affect the national trend estimate, which takes into account all polling?