You may not know it, but the winner of this year’s Super Bowl will be a pretty reliable predictor of how the stock market performs in 2016. And with four teams left and the big game slated for Feb. 7, we’ll know pretty soon.

There’s a long and kind of complicated history to the method—dubbed the “Super Bowl predictor” or “indicator”—that goes back to when there were separate football leagues, but now it boils down to this:

If a National Football Conference team wins the Super Bowl, then the Dow Jones Industrial Average will rise in 2016. If an American Football Conference team wins, then the index will fall.

Four teams are left in the playoffs scheduled for Sunday: Arizona and Carolina in the NFC and New England and Denver in the AFC. So a Super Bowl win by the Cardinals or Panthers would signal a rise in Dow stocks in 2016, while a Patriots or Broncos victory would point to a drop for the year.

This phenomenon has an amazing success rate: 82%. In fact, the winning NFL team has tracked how the markets fared the last seven years in a row, as well as for 40 of all 49 Super Bowl years, according to the Wall Street Journal. Take 2015 for example: The New England Patriots won, and the Dow fell 2.2% for the year.

Robert H. Stovall, an analyst who’s popularized the predictor, admits it has no grounding in fact. “There is no intellectual backing for this sort of thing,” he said in an interview with the Journal, “except that it works.”

Stovall, nearly 90, credits the idea for the indicator to a sportswriter, Leonard Koppett, who discovered the correlation back in 1978, according to CNBC. And although Stovall told the Journal he isn’t rooting for a specific team to win the Super Bowl, it’s a good bet he wants either the Arizona Cardinals or Carolina Panthers to be victorious.

Why? Because Stovall said he wants to see stocks rise in 2016.

The NFL declined to comment.