Those of you who tire of my periodic whinging about the spinning frenzy engaged in by GOP partisans shortly before every election must forgive me: it’s getting really, really bad right now. Just looking at RealClearPolitics’ front page at the moment, there’s “Things Are Better For Republicans Than They Dreamed” by Ed Rogers; “How Reid Doomed Democratic Senators” by Jonah Goldberg; “Republicans Begin To Pull Away” by Joseph Curl; and “Desperate Dems Turn to Racial Attacks” by Ellen Carmichael. I’ve never understood why conservatives think predicting total victory in all states has value; maybe they really do think “enthusiasm” is what politics is all about, and some of them clearly don’t worry about their future credibility.

It’s not just stone partisans, however. Some MSM types are really getting into the “wave” and “Big Mo” talk. There’s Politico‘s Alex Isenstadt with “House Democrats Fret Debilitating Losses” and Balz and Craighill’s big poll-driven WaPo piece from yesterday, “Midterm Momentum Belongs To GOP.”

That last piece clearly aroused Nate Silver and Harry Enten of FiveThirtyEight to reprise their warnings about the frequently illusory character of “momentum” in politics:

You might be hearing that Democrats or Republicans have “momentum” heading into the final week of the 2014 campaign. On Tuesday, for example, a Washington Post headline asserted “Midterm momentum belongs to GOP.” That was based on a generic ballot poll showing a 6 percentage point Republican lead. But later in the day, a Fox News generic ballot poll came out showing Democrats up by 1 point instead — Fox had previously shown Republicans ahead.

This pattern — or rather, this lack of a pattern — has been typical throughout this election cycle. Whenever one party seems to be gaining an advantage, the other party has countered it with some good news of their own.

Republicans have maintained a narrow overall edge in their quest for a Senate majority, but the magnitude of their advantage hasn’t changed much throughout the campaign. When the FiveThirtyEight model launched Sept. 2, it gave Republicans a 64 percent chance of winning Senate control. In our latest forecast, their chances are 62 percent. They’ve never been higher than 66 percent or lower than 53 percent.

We’ve critiqued the media’s use of the term “momentum” before. It’s one of those clichés that’s easy to misapply.

In many elections — unlike this one — the polls have consistently drifted toward one party for some extended period of time. Their was a sharp break toward Democrats in Senate polls throughout September and early October 2012, for example.

Even in these cases, however, the m-word should be applied carefully. When used in a more technical sense, momentum implies positive serial correlation. What the heck does that mean? It means you’re predicting the trend will continue in the same direction. If you say that the Dow Jones Industrial Average has “momentum” because it has risen from 16,000 to 17,000 points, you’re suggesting it will continue to go up.

The stock market doesn’t behave like this; it’s much closer to being a random walk, meaning it’s equally likely to go up or down on any given day. Nor does it matter in which direction the movement has been in the past. If the stock market rises from 16,000 to 17,000 points, it’s roughly as likely to revert back to 16,000 as to continue rising to 18,000.

For the most part, polling is the same way. There are some exceptions to this…mostly involving primary elections and cases where the polling is out of step with the “fundamentals” of the race. But to a first approximation, you should assume there isn’t any momentum in the polls.

We’re all susceptible to the “momentum” illusion; it’s overused incessantly in sports, for example. And there are certain elections (e.g., 1980 and 2012 Senate races) that reinforce the hope or fear that close contests will all break in the same direction thanks to one party’s “momentum.” But for the most part, it’s the imagination taking over from the brain and supplying missing evidence for what we want to transpire.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.