Big Data Poll finds a close Michigan Senate race as our margin edges to D+3.3

A new Big Data Poll survey for the Public Polling Project, fielded September 22-24, finds the Michigan Senate race close. Among 678 likely voters, it has Democrat Abdul El-Sayed at 46.7 percent and Republican Mike Rogers at 42.1 percent. Among 725 registered voters in the same survey, it has El-Sayed at 45.4 percent and Rogers at 41.0 percent. Both gaps are small enough, for samples of that size, that the poll does not separate the two candidates with confidence.

The numbers fit what our model already expected. Our model gives El-Sayed a 72 in 100 chance of winning the open seat held by Democrat Gary Peters, the same as in our run earlier this evening. Rogers's chance stays at 28%. The only movement is in the expected margin, which our model now puts at D+3.3, down from D+3.4. Its range of plausible outcomes, from the 5th to the 95th percentile, runs from R+6.1 to D+12.8, against R+6.1 to D+12.9 before.

That range is the more useful figure. It spans a Rogers win by about six points and an El-Sayed win by nearly 13, which is why a four-point edge in one survey changes little. A poll that lands close to our model's expected margin mostly confirms it.

The seat matters for the chamber. Our model gives Democrats a 56% chance of winning Senate control and projects them at 50.8 seats on average. Democrats need 51 seats for a majority; Republicans need 50, because the vice president is a Republican and a 50-50 tie goes to them. With the election 39 days away, our Michigan forecast has now held in a narrow band through several days of new polling.