InsiderAdvantage has Pappas up eight in New Hampshire, and our forecast stays at 85

An InsiderAdvantage survey of 1,200 likely voters in New Hampshire, fielded September 16-18, puts Democrat Chris Pappas at 48 percent and the Republican at 40 percent in the state's open Senate race.

Our model gives Pappas an 85 in 100 chance of winning the seat, against 15 percent for Republican Scott Brown. That is where the race stood in our previous run, at 10:32 a.m. ET on September 18. The mean margin in our simulations is now D+10.9, against D+11.0 before, and the spread is essentially identical: our 5th-to-95th percentile range runs from R+6.4 to D+28.2, compared with R+6.3 to D+28.3. The new poll confirmed the existing picture rather than changing it.

That range is the part worth holding onto. Our model still treats outcomes from a mid-single-digit Republican win to a Democratic margin near 30 points as inside the plausible band 46 days out, which is why an eight-point result in a single survey moves the forecast by a tenth of a point and nothing more.

The seat matters to the wider picture. Our model gives Democrats a 51 in 100 chance of Senate control and Republicans 48 percent, with a mean of 50.5 Democratic seats. Democrats need 51 seats for control and Republicans need 50, because the vice president is a Republican and a 50-50 tie goes to the Republicans. The House is far less close in our numbers: 97 percent for Democrats, 3 percent for Republicans, with a mean of 242.8 Democratic seats against the 218 needed. One caveat on that House figure is ours to own. Our simulation correlates error nationally, by census division, by state and by district, but we have no data to correlate demographically similar districts wherever they sit, so our House control probability is marginally firmer than a fuller error model would leave it.