The Science of Momentum: Does a Win Today Predict a Win Tomorrow?

If your favorite team or player wins on a given day -- especially if it's a landslide win, then it's likely that "momentum" gets thrown around by people previewing the next event.

Winning in any activity often gets used to build confidence for the next contest. Along with sports commentators, "momentum" is frequently used by stock analysts talking to investors, politicians talking to supporters, and executives talking to employees and other stakeholders.

For better or worse, momentum is one of those concepts that's sticky in our heads. We're evolved to see patterns -- like figuring out "who's hot" and "who's not" -- partly to help us anticipate the future.

In a new study that's set for publication in the March edition of Economics Letters that I completed with Vince Mihalek, we look at the questions of (1) whether momentum from winning one game influences the probability of winning the subsequent game and, more specifically, (2) whether the margin of victory -- for teams winning a given game -- influences the subsequent game's outcome.

On the surface, we found a positive correlation between the margins of victory in the two-game sets that we studied and this is the kind of pattern that would lead people to conclude reasonably that momentum from one game to the next is important.

Once we controlled for the quality of teams competing against each other, though, to take into account that some teams are better than others, then any effect of "momentum" no longer appears. As we write in the paper, (1) winning a given game showed no specific boost for winning the next game and (2) "running up the score" also showed no influence on the subsequent game's outcome once the quality of the respective teams was considered.

The unique sample of games that we studied were 458 two-game series -- looking at the influence of Friday games on the outcome of Saturday games -- played in the NCAA Division 1 Western Collegiate Hockey Association (WCHA) over a recent six-year period.

If momentum effects were to exist at the level of one game or one day to the next, the WCHA schedule would be the place where you would find it since the same two teams play each other in the same arena for two games in a row with the same amount of recovery time (approximately 22 hours) between the two games.

Unsurprisingly, we do find that the quality of teams is a significant predictor for whether a team that wins the first game of a series also wins the second game a series. In other words, good teams often appear to be on a streak but the closer analyses show that the streaks happen because the teams are good and not because of any underlying "momentum."

One take-away from the findings is that "every game offers a fresh chance" to compete. This can be encouraging, depending on your perspective, since it also means that losing a given game has no specific momentum effect on losing or winning a subsequent game.

Likewise, while some sports fans have been known to fear that their team might "use up" too many runs in a given game, our study shows neither a positive nor a negative influence of a given win's margin of victory on the outcome of the subsequent game. Running up the score doesn't help for the next game but it also -- for the more nervous amongst us -- waste up performance that might otherwise be rationed across games.

Co-author Mihalek and I approached this study as an open empirical question. In fact, Mihalek -- a four-year player on Cornell's nationally-ranked Men's Ice Hockey program -- knew from experience that coaches and players routinely go into two-game weekend sets with an expectation that the outcome of Friday night games influences the probability of winning the next game even when the opponents for the two games are different.

Mihalek elaborates that "Lots of coaches preparing for two games in a weekend against different opponents will tend to focus more practice time on the first of the two opponents, partly because of the belief in momentum."

Most of us, of course, have not played -- and won't ever play -- hockey at an elite level and so -- who cares about the new study?

Partly for the same reason that most of like watching Olympic sports and other events that we'll never attempt to personally tackle, sports provides a model domain for us to draw generalizable lessons. In this case, the presumption in most cases is that (1) momentum is important in sports and (2) it should consequently be assumed to be important outside of sports.

Our new study debunks the premise that momentum exists at the level of one game or night to the next.

Consistent with studies showing that belief in momentum can inspire overconfidence and overly risky decision-making, Mihallek and I offer a cautionary tale with the benefit of advanced statistics that gets past surface observations.

Our findings indicate that people are best served by focusing on overall quality so that "momentum happens" as an artifact or side effect of being good.

Kevin Kniffin is a behavioral scientist at Cornell University who studies topics that are relevant for everyday work and life. Read Kniffin and Mihalek's study in full here.