By finishing second (to Jason Day) in the PGA Championship on Sunday, Jordan Spieth completed a remarkable run at golf’s major championships this season. He won two major tournaments (the Masters and the U.S. Open), placed second in another (the PGA), and — in his worst showing — tied for fourth at the British Open. It was the third time since 19581 that a player finished no worse than fourth in any major during a season.
Last week, my colleague Andrew Mooney used a metric called z-scores (which measure how many standard deviations a player’s score was from the mean2) to examine where Spieth’s overall PGA Tour season — including both majors and the tour’s more pedestrian tournaments — ranked among other golfers’ seasons since 1970. Going into the PGA, he was on pace for the 12th-best single season in that span, and he was the top-ranked player not named Tiger Woods or Jack Nicklaus. (Pretty heady company!)
But we can also use z-scores to measure where his cumulative performance at the majors this year ranks. The — admittedly predictable — result is that Spieth’s 2015 majors campaign stands as one of the greatest in the sport’s history.
Here’s how it works: In a given tournament, a player’s performance can be converted into the probability that he would win the average major with his z-score. For example, Spieth’s -2.20 z-score at the PGA last weekend would be good enough to win about 40 percent of all majors staged since 1958. Therefore, he gets 0.40 shares of a major for the performance, even though he didn’t actually win.
Of course, this methodology can add up to more than 100 percent of a victory for majors featuring multiple great performances. The famous “Duel in the Sun” between Nicklaus and Tom Watson at the 1977 British Open was so epic, for instance, that the system above awards 2.1 total “generic majors” to the field. To correct for this, we can also compute an adjusted version that isn’t allowed to assign more than 1.0 combined shares of a major to any given tournament’s field, no matter how dominant — or dubious — the performances of its leaders. (According to this adjustment, Spieth’s 2015 PGA Championship earns him just 0.18 share of a major, since the field total also needs to clear room for the performances of Day, Branden Grace and others.)
Depending on which version you use, Spieth’s 2015 season either ranks fourth overall since 1958 (without the adjustment), or 11th (with the adjustment).
My preference probably lies with the unadjusted version, simply because a player can’t control whether he shares the stage with another dominant performance (and z-scores already account for his score relative to the field average). But no matter the method, it’s clear once again that Spieth’s 2015 season deserves a place among golf’s most brilliant achievements.