Solid Brown Lead in Final MA-Sen Models

01/18/2010 07:31 pm ET | Updated May 25, 2011

Republican Scott Brown holds a lead in all 18 alternative models of the Massachusetts Senate race polls, now including all polls released through 6:00 p.m. Monday. Our standard trend estimate puts the race at a 6.2 point Brown lead over Democrat Martha Coakley. The less sensitive alternative linear model puts the Brown lead at 7.3 points. Across all models, Brown leads by between 1.0 and 8.9 points. Three quarters of the estimates have Brown ahead by 4 points or more. 

Brown built this lead over the past week of polling with only some tentative sign of the trend flattening over the weekend. Of course the last available polls were completed Sunday evening so we do not know if any movement has occurred on Monday.

Here is a brief review of the polls and the various models estimated. First, the polls without any trend estimates:
One of the unusual features of the MA polls is the large number of leaks from Coakley's internal polling. No one leaks without a reason, and her leaks have been consistently better for her than other polling taken at the same times (with one exception). Past analysis has found that internal polls are typically about 5 points better on the margin for the leaker than are independent polls, but that the internal polls do track the trend rather well. This raises a question of how to treat Coakley's polls. Below, I estimate the models both with and without the leaks included, so we can see their potential impact. I have not discounted them for the historical five point bias with internal polls.

First, let's estimate the local regression models that are our standard here at Pollster. These are not identical to the dynamic charts because here I am estimating the Dem minus Rep margin while our charts estimate each candidate separately. I estimate the standard model, a more sensitive and a less sensitive version, and then repeat with the leaked polls included.
With the limited number of polls, the local its are not as smooth as in our usual trends with dozens or hundreds of polls. They may also be more sensitive to outliers. That is one reason to check the effect of sensitivity.  For the three models without leaked polls, the sensitivity matters a bit for the trajectory but hardly at all for the endpoints.  When internal polls are included, the trends end up a couple of points more Democratic, though still put Brown ahead in the end. (The more sensitive estimate touches dead even but that is due to a day with only an internal poll. The sensitive estimator chases that but then moves back down.)