A new poll released Tuesday shows Democratic Senate candidate Elizabeth Warren with a narrow edge in the Massachusetts race, contradicting several other polls released in recent weeks that showed Republican Sen. Scott Brown in the lead.
The new poll, conducted March 16-18 by the Democratic-leaning firm Public Policy Polling with automated polling methods, found Warren leading Brown by a 46 percent to 41 percent margin. The result is within the poll's 3.2 percentage point margin of error, which applies to the results for each candidate individually.
Other recent polls have found mixed results in the race. Three of four other polls conducted since the beginning of February found Brown leading Warren, while the fourth found Warren leading within the poll's margin of error. Most recently, a Western New England University survey found Brown leading by an 8 percentage point margin, while Rasmussen Reports found Brown had a 5 percentage point lead.
In addition to differing from other recent polls, the PPP survey also stood out in its finding that Brown's position was less favorable among independents. Although Brown does lead among independents in the PPP poll by a 12 percentage point margin, his leads among independents in the other polls conducted since the beginning of February range from 21 percentage points to 38 percentage points.
While it's possible that the varied results among recent surveys are due to real changes in the dynamics of the race, it's more likely -- given the short time periods involved -- that changes from poll to poll are a result of a combination of statistical variation and differences in sampling, both of which can make it difficult to determine the "real" leader in very close races such as this one.
The PPP survey differs from other recent surveys in both its method for calling and choosing its sample. PPP and Rasmussen used automated calling, while all of the other recent surveys used live interviewers. Unlike Rasmussen and Western New England University, which used random digit dialing to select the numbers they called, PPP drew its sample of 936 likely Massachusetts voters from registered voter lists. The surveys also vary in whether they polled registered or likely voters, and how they defined likely voters where applicable.
According to the latest HuffPost Pollster trend estimate, which takes into account all available public polling and gives greatest weight to the most recent polls, Brown has a small 47.6 percent to 43.2 percent lead.
Although polling on the race has produced differing results, it is clear that the Warren-Brown race is close, with the precise leader and margin difficult to ascertain through the statistical noise and different polling methods.