Our Ohio Senate estimate for Brown drops 8.3 points in four days

Our model now gives Democrat Sherrod Brown a 71 in 100 chance of winning the Ohio Senate special election against Republican Sen. Jon Husted. In our September 29 run, at 6:02 AM ET, that figure was 80%. The change is 8.3 points of Democratic win probability toward the Republican over four days. The rounded figures overstate it slightly.

Our expected margin narrowed from D+4.7 to D+3.1. Our 5th-to-95th percentile range now runs from R+6.0 to D+12.1, compared with R+4.5 to D+13.9 in the earlier run. This partly reverses movement toward Brown that we reported earlier.

Five Ohio polls in our data were fielded between September 22 and October 1. Every one shows Brown ahead by less than the D+4.7 our model expected in the earlier run. A Big Data Poll survey for the Public Polling Project, fielded September 26-27, had Brown at 46.3% and Husted at 42.6% among 680 likely voters. Among 735 registered voters, it had Brown at 45.2% and Husted at 41.2%. A Suffolk University poll for USA Today, fielded September 23-27, had Brown at 46.6% and Husted at 44.0% among 500 likely voters. An InsiderAdvantage survey of 1,200 likely voters, fielded September 28-29, had Brown at 44% and Husted at 43%. A New York Times/Siena survey of 616 likely voters, fielded September 22 to October 1, had Brown at 48.76% and Husted at 46.09%.

All five polls describe a close race. Our data does not break down how much each poll contributed to the shift. It also does not say whether anything other than polling moved the estimate.

Nationally, our model gives Democrats a 55% chance of winning Senate control. Democrats need 51 seats for control, and Republicans need 50. Our model projects an average of 50.7 Democratic seats.