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Jordan Spieth and the Grand Slam: Virtually no chance, popular data analysis site concludes

June 24, 2015

Jordan Spieth in all likelihood will not win the Grand Slam. This is not a bold prediction, of course; no one has ever won the Grand Slam.

But FiveThirtyEight, the blog founded by Nate Silver, has run its information through its DataLab and came up with this:

"No matter how you cut it, the odds of Spieth finishing off the Grand Slam are still fairly low — about 1 percent, if the probabilities above are any kind of guide."


Silver, a statistics and analytics expert, is the man who came to fame largely on the basis of his accuracy in predicting outcomes in the 2008 elections. He correctly predicted the winner of 49 of 50 states in the presidential election and all 35 U.S. Senate races.

FiveThirtyEight might be stating the obvious in the case of Spieth and the Grand Slam, but it did consider substantially more information than the fact it's never been achieved. Among the information it is is what is called a Z-Score, developed by Bill Barnwell, who describes it this way:

"Z-Score measures a particular performance against the entire field of values, accounting for both the average result and the full range of performances from top to bottom. It does a great job in capturing how much better or worse an individual score was versus the entire population, producing a value that translates across different tournaments, locales, and generations."

FiveThirtyEight did one other calculation, to project how many majors Spieth will win in his career: Just under 12. But it emphasizes that that is a mean projection. "The variance around it means there are plenty of scenarios in which he wins more than 12," Neil Paine of FiveThirtyEight wrote.