Close PA-10 poll trims our margin for Stelson but not the shape of the race

A Franklin & Marshall College survey of 378 registered voters, fielded September 9-20, puts Democrat Janelle Stelson at 47% and Republican incumbent Scott Perry at 44% in Pennsylvania's 10th District. That three-point separation, on a sample that small, describes a close race rather than a clear edge.

Our model now gives Stelson an 82 in 100 chance of winning the seat, with a mean margin of D+8.2 and a 5th-to-95th-percentile range running from R+6.4 to D+22.9. Before this run, our forecast had her at 86% with a mean margin of D+9.7 and a range of R+5.0 to D+24.3. The new poll moved the numbers modestly in Perry's direction and widened the downside tail slightly. It did not change what the forecast has been saying: Stelson is favored, and a Perry win is well inside the range our simulations produce.

The gap between the poll and our projected margin is worth stating plainly. Our average leans on more than this district's own polling; the national generic ballot stands at D+8.3 across 30 polls in a 45-day window. A single 378-respondent survey of registered voters pulls that estimate, but not far.

Nationally, our model gives Democrats a 98% chance of reaching a House majority, with a mean of 245.8 seats against the 218 needed. One caveat is ours to own: our simulation draws error at the national, census-division, state and district levels, but we have no data to add a term linking demographically similar districts across state lines. Without it, our House control probability is marginally firmer than a fuller accounting would leave it. We cannot measure how much, so we are not adjusting the figure.