Why voters need to forget the latest polling data

Glance quickly at polling data published over the last month and you might think that Democrats had substantially improved their prospects after Labor Day, only to squander those gains as September wound down. That would be the wrong conclusion.

It’s tempting to try to figure out whether one party or the other has momentum. I caution against playing that game. The problem? Unless there are massive shifts in the polls, even the best data won’t tell us much.

For example, the latest Senate forecast by FiveThirtyEight has shifted since Sept. 1 from Democrats having a 68% chance of a majority up to a peak of 71% and down to 67% right now. That may seem like real movement, first toward Democrats and then toward Republicans. But it could easily just be statistical noise. The political landscape certainly has shifted markedly since spring, when a Republican landslide seemed likely. But it probably hasn’t pingponged in just the last few weeks.

What, then, explains why the numbers are bouncing around? For one, individual polls each have a margin of error that could move results a few percentage points in either direction. Also, different polling outfits, using slightly different methods, can favor one candidate or the other, and even well-constructed polling-based forecasts can’t always correct for that.

It could be that a few more Republicanfriendly surveys were conducted in the second half of September after a few more Democratic-friendly ones dropped in the first half of the month, creating the illusion of change. Every polling average contains a host of assumptions — which surveys to include, whether and how to weigh and adjust them, and more — and any forecast contains an even wider array of built-in assumptions that might not apply in this election cycle. All of that uncertainty totally swamps small movements in forecasts.

I’m a big fan of forecasts made by outlets such as FiveThirtyEight, but be careful about mistaking mathematical expressions for clarity. Polls can give us a general sense of where things stand, but they shouldn’t be interpreted as ironclad predictions. For that matter, expert analysis from places such as Cook Political Report and Inside Elections is great, but also best used to give a general sense of where things stand rather than anything definitive.

I’m also seeing a lot of assertions based on very limited data that the Senate majority will come down to a single state, usually Pennsylvania. In fact, there are still quite a few Senate seats — and far more House seats — whose outcomes are uncertain.

The states won’t all necessarily move together; for example, Senate races in Georgia and Wisconsin could shift a few points toward the Republicans while Pennsylvania and Nevada shift in the opposite direction.

Sure, if the entire nation moved decisively in one direction over the last few weeks, then we could be relatively certain that the elections that appear closest right now will all go toward the candidates benefiting from that movement.

But don’t count on there being one overarching trend. State and local issues, campaign strategy and the skills of individual candidates could determine the outcomes of some contests in ways that aren’t easy to predict at this stage. We don’t know whether Hurricane Ian or fluctuations in gas prices or late-breaking border issues will have any electoral effects. But they, or something we don’t even know about yet, still might matter.

Barring any big changes, it is starting to look like we will enter election week with a more or less equal chance of one of three possible outcomes: Republicans gain majorities in both the House and Senate; Democrats maintain control of both chambers; or Republicans win a House majority but Democrats still have 50 — or more — senators. Beyond that, we’ll just have to wait for the results.