Super Bowls and Stock Markets

The Super Bowl “theory” links U.S. stock market performance to the results of the championship football game, held each January since 1967. It holds that if a team from the original National Football League wins the title, the stock market increases for the rest of the year, and if a team from the old American Football League wins, the stock market goes down.

Economist Paul M. Sommers of Middelbury College in Vermont has analyzed the data for the years from 1967 to 1998. He reports his findings in the May College Mathematics Journal.

Sommers defined six variables, one for each of the divisions (Eastern, Western, Central) of the National Football Conference (NFC) and the American Football Conference (AFC). If the Super Bowl winner was from a particular division, the relevant variable was assigned the value 1; otherwise, it was 0. The dependent variable (DJIA) denoted the percentage change in the Dow Jones Industrial Average between the closing average on the Friday before Sunday’s championship game and the closing average on the last day of that calendar year.

Super Bowl winners and changes in the Dow Jones Industrial Average (DJIA), 1967-2000:

Year Winner Conference Current Division Total Points Percentage
Change in DJIA
1967 Green Bay NFC Central 45 +8.38
1968 Green Bay NFC Central 47 +4.98
1969 New York Jets AFC Eastern 23 -13.52
1970 Kansas City AFC Western 30 +5.11
1971 Baltimore AFC Eastern 29 +5.26
1972 Dallas NFC Eastern 27 +12.50
1973 Miami AFC Eastern 21 -18.14
1974 Miami AFC Eastern 31 -26.77
1975 Pittsburgh AFC Central 22 +29.39
1976 Pittsburgh AFC Central 38 +8.07
1977 Oakland AFC Western 46 -15.46
1978 Dallas NFC Eastern 37 +3.77
1979 Pittsburgh AFC Central 66 +0.15
1980 Pittsburgh AFC Central 50 +11.17
1981 Oakland AFC Western 37 -6.93
1982 San Francisco NFC Western 47 +23.85
1983 Washington NFC Eastern 44 +18.21
1984 L.A. Raiders AFC Western 47 -3.78
1985 San Francisco NFC Western 54 +26.02
1986 Chicago NFC Central 56 +23.92
1987 New York Giants NFC Eastern 59 -7.74
1988 Washington NFC Eastern 52 +10.74
1989 San Francisco NFC Western 36 +23.17
1990 San Francisco NFC Western 65 +2.91
1991 New York Giants NFC Eastern 39 +19.16
1992 Washington NFC Eastern 61 +2.11
1993 Dallas NFC Eastern 69 +13.42
1994 Dallas NFC Eastern 43 -2.81
1995 San Francisco NFC Western 75 +32.64
1996 Dallas NFC Eastern 44 +22.32
1997 Green Bay NFC Central 56 +18.10
1998 Denver AFC Western 55 +20.61
1999 Denver AFC Western 53 +22.85
2000 St. Louis Rams NFC Western 39 ?

Here’s Sommers’ mathematical model:

DJIA = b0 + b1AFCE + b2AFCC + b3AFCW + b4NFCE + b5NFCC + b6TOTALPTS + b7TOTALPTS*ROOTS + e.

TOTALPTS gives the total number of game points, and TOTALPTS*ROOTS represents an “interaction term” where ROOTS equals 1 for a team from the original National Football League, including Cleveland, Indianapolis (formerly Baltimore, and Pittsburgh); otherwise, ROOTS is 0.

Sommers’ model suggests that the stock market posts a significantly higher gain if the Super Bowl winner is from the National Football Conference Western Division. Moreover, the higher the combined team point totals are, the lower the percentage change in the Dow Jones Industrial Average.

At the same time, the model suggests that the Super Bowl theory’s predictive power has declined precipitously in recent years. The victory by the Denver Broncos in 1998 implied that the percentage change in the Dow Jones Industrial Average would be –20.85 percent. In fact, the Dow closed out the year 1998 up 20.61 percent.

In general, the explanatory power of the model has fallen from nearly 82 percent to less than 53 percent in the last decade. Factoring in the 1999 results, when the Denver Broncos defeated the Atlanta Falcons, makes the fit even worse–only 46 percent.

“Despite the Super Bowl theory’s surprisingly strong early record, reading the sports page now is not making it any easier to read economic tea leaves,” Sommers concludes.

What accounts for the surprisingly strong predictive power of the Super Bowl theory in the early years? “Statistical fluke,” Sommers suggests.

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