The MLB All-Star Game's home-field advantage prize is massively important

"The MLB All-Star Game: This One Counts."

This is the message Major League Baseball has pushed almost endlessly for the last decade every time the Midsummer Classic rolls around. That's because the MLB All-Star Game does decide something important: Home-field advantage in the World Series, which on the surface, seems like an odd thing to attach to an exhibition game in which players routinely get a single at-bat before spending the rest of the game on the bench.

As a rule, the winning league in the All-Star Game is awarded home-field advantage in the World Series, a change instituted for 2003 and beyond to give everyone something to play for as opposed to… well, whatever myriad reasons players had for competing in the All-Star Game before that. (The change was a reaction to the much-lampooned 7-7 tie in the 2002 All-Star Game.)

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Analysts often complain about giving the All-Star Game this kind of power. After all, if a team posts the best record in baseball, shouldn't it get home-field advantage instead of having it be determined by the bloops and variances of a single game held in mid-July featuring players from other teams who probably aren't trying all that hard anyway?

But just how important is home-field advantage in the World Series? Let's do some quick and dirty number crunching to find out.

We'll start with the games just since the rule change. From the 2003 World Series onward, there have been 50 World Series games; the home team has won 30 of those, a nice and tidy .600 winning percentage. What's more, of those 10 series, the team with home-field advantage has won the championship seven times. If you add in the three prior World Series to get a rough idea of the decade, the winning percentage for home teams jumps to .630, or 43 of 68 games. All of the World Series-winning teams from those three years had home-field advantage.

Going further back, the trend still holds. The 1990s featured 48 World Series games, with home teams prevailing in 28 of them, a .575 winning percentage. That decade was even crueler to the road team than the 2000s. Only two of the nine teams that had home-field advantage lost the World Series that decade: Atlanta in 1992 and again in 1999. All told, from 1990 onward, home teams have a .610 winning percentage in the World Series, or 71 out of 116 games.

Pushing back even more, in the 1980s, there were 59 World Series games; the home team won 38 of them, a .640 winning percentage. Just like the 1990s, only twice did a team with home-field advantage lose the Series: The Padres and the Yankees, in 1984 and 1981, respectively. Added to the previous decades, from 1980 onward, the home team in the World Series has won a staggering 109 out of 175 contests, for a .620 winning percentage.

No matter how many years you go back, home teams in the World Series maintain a winning percentage just around .600. Home-field advantage occasionally has hiccups — in the 1970s, just three of the 10 teams with home-field advantage won the World Series — but since 1980, 25 of 32 teams with home-field advantage have taken the championship, a winning percentage of .780. There's no doubting that the team at home in the World Series has a leg up on the visiting squad.

How sure of that can we be? As one test, we can check to see what the expected winning percentage would be according to runs scored and allowed by the home team, otherwise known as the Pythagorean expectation. Since 2003, home teams in the World Series have scored 219 runs and allowed 183. Plug those numbers into the Pythagorean expectation formula, and you get an expected winning percentage of .589, or not far at all from the actual .600.

The home team has won the last seven Game Sevens in the World Series: 2011 (St. Louis), 2002 (Los Angeles nee Anaheim), 2001 (Arizona), 1991 (Minnesota), 1987 (Minnesota), 1986 (New York Mets), and 1982 (Cardinals). In all seven of those series, the home team was down three games to two going into Games 6 and 7, and in all seven series, the home team rallied and won those two final home games.

In 2011, 2002, and 1986, having the final at-bats in Games 6 and 7 proved crucial to winning. The Cardinals rallied from being down 7-4 in the seventh inning of Game 6 in 2011 to Texas, winning on a walk-off home run in the 11th inning. The Angels came back from a 5-0 deficit with just nine outs left in Game 6 in 2002 against San Francisco to win 6-5. And the Mets shocked the Red Sox in 1986 by tying Game 6 in the eighth, then rallying from two runs down in the 10th to win 6-5.

Home-field advantage does matter, which is something baseball's higher-ups probably know all too well. Should that kind of gift be given to whichever All-Star team, featuring several players who won't even be in the World Series, tries hardest in a single July game? It's hard to argue for that. Though it's better than MLB's old system: Before 2003, leagues simply alternated home-field advantage every year.