Senate forecast: Toss-up or tilt GOP?

Our March forecast projected a Republicans gain of 5.8 seats. You’ll no doubt notice the decimal place; how can a party win a fraction of a Senate seat? It can’t, but our forecasts are probabilistic; a gain of 5.8 seats is the total you get by summing the probabilities from each individual race. Because 5.8 seats is closer to six (a Republican takeover) than five (not quite), we characterized the GOP as a slight favorite to win the Senate.

The new forecast is for a Republican gain of 5.7 seats. So it’s shifted ever so slightly — by one-tenth of a seat — toward being a toss-up. Still, if asked to place a bet at even odds, we’d take a Republican Senate.

Of course, it can be silly to worry about distinctions that amount to a tenth of a seat, or a couple of percentage points. Nobody cares all that much about the difference between 77 percent and 80 percent and 83 percent. But this race is very close. When you say something has a 47 percent chance of happening, people interpret that a lot differently than if you say 50 percent or 53 percent — even though they really shouldn’t.3