What does it usually mean?
The impetus gained by a moving object.
What does it mean in this election?
The theory that, if a candidate or party has gained ground in recent polls, that trend should continue in the next results. Known as “The Big Mo” in the US, it’s often deployed as a self-evident truth by journalists desperate to extract something actually interesting from statistically insignificant shifts in poll numbers.
Where did it come from?
It originated (and continues to this day) in sports coverage, where a team or player is deemed to benefit from the effects of a good run of results. First used in politics by George H W Bush after he won the Iowa caucuses in the 1980 Republican presidential primaries. After his win, Bush Senior said, "Now they will be after me, howling and yowling at my heels. What we will have is momentum. We will look forward to Big Mo being on our side, as they say in athletics." He lost to Ronald Reagan.
Does momentum really exist?
Nate Silver, the most respected electoral analyst in the US, says no. "In general elections, the direction in which polls have moved is not predictive of the direction in which they will move," he wrote in 2010.
“Thus, it is usually wrong to say that a candidate is gaining ground in the polls – present tense – or that her position is improving. Instead, you should say that the candidate has gained ground or that her position has improved.”
So it’s all a fairytale?
Yes. It’s often suggested that if successive polls in the run-up to an election show a party increasing its percentage, then that trend will continue upwards when the actual vote takes place. There is no empirical evidence that this is true.
So why do so many people in politics believe it?
Think of it as part of the natural human impulse to find structure and narrative in the meaningless void of existence. As Silver says: “We can look at a pretty chart, and see the lines converging toward one another: our brains tend to assume that they are eventually bound to cross. But at least as often, they do not. And a candidate’s ‘momentum’ proves to be ephemeral.”
Will we hear it much in this election?
Undoubtedly.
