Last night's Slate Scorecard update reviewed the relatively recent polls showing new momentum for Iowa gubernatorial candidate Democrat Chet Culver, but I want to take a moment and review two things readers should know about the averages in the Slate Senate Scorecard.
First, readers should know that the averages in our new Pollster.com scorecards and summary tables (Senate and Governor) replicate the averages that we have been providing to Slate but extend them to every race for Senate and Governor. They use the last five polls in a race, but -- unlike the averages that currently appear on our chart pages -- they exclude surveys based on internet panels.
Second, regular readers of the Slate feature should be familiar with the big blue "momentum shift" meter that sits atop the Senate scorecard. It has pointed in the Democratic direction since September 15, meaning that recent trends across all 13 of the competitive Senate have been shifting in a Democratic direction. These averages summarize the results of over 190 polls conducted in those states since the summer. Some readers have wondered about why the meter has been seemingly frozen in place for over a month. Can a momentum "shift" really continue for a full month?
The numbers say it can. As the table below shows, the average Democratic lead across the 13 states we track for Slate has nearly doubled, rising from 1.9% to 3.7% since early September. The net gain is greater if we remove the Connecticut (for which we calculate the average deficit of Democrat Ned Lamont to Sen. Joe Lieberman).
And those gains have been spread out over a large number of races, with net gains in 10 of 13 races. The largest increases on the margin have been in New Jersey (+7.8), Ohio (+5.4) and Tennessee (+5.4).
The current scoreboard indicates a 49 to 49 tie in the Senate if all trends continue (assuming that Joe Lieberman caucuses with the Democrats), with Missouri and Tennessee still classified as "toss-up" races. When we started tracking for Slate on September 1, Republicans held a 50 to 46 lead. These numbers tell the story of what happened since.
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