What’s wrong with Rory?

Rory McIlroy missed his second cut in a row this week at the Scottish Open. A flurry of news articles and social media posts are likely to follow in the next couple days wondering what’s wrong with Rory. “Where has the lad’s game gone?!” cries a devoted Rory fan — “You can cross him off the list of potential contenders next week.”  tweets a Golf Channel pundit — “It’s simple, really. The deadlifts have finally done him in; this is causing Rory to slump a bit through impact, losing the angle, missing right.” analyzes Brandel.

In my opinion, however, there is nothing wrong with Rory. My argument is simple: golf scores are really random. Below is a density plot of Rory’s scores over the last 2 years.

This is how I like to think of a golfer’s performance; Rory’s score each day (no matter what course he’s on!) is a draw from the above distribution which has mean 2.3, and standard deviation 2.7. Better golfers will have distributions with higher means, and more consistent golfers will have distributions with smaller standard deviations. So, when Rory shoots 2 shots worse than the field, I don’t panic; this isn’t that unlikely (it should happen about 6% of the time).

So, back to Rory’s MC-MC performance over the last 2 weeks. How often should that happen for a player of Rory’s caliber? Well, my sample of data contains the last 2 years, in which Rory played 38 events (I think). I simulate these 38 events 10,000 times (doing exactly what I said above; each round is a draw from the above distribution). I deem Rory to have missed a cut if the sum of his first 2 rounds is less than 0 (so he lost to the field, which should, roughly speaking, result in a missed cut). In 35% of the simulations, Rory had back-to-back MCs at some point in the 38 event sequence.

This is Rory’s first stretch of consecutive missed cuts since May 2015. So, in the 2 year sample I’ve considered, Rory has missed back-to-back cuts on exactly one occasion. This is not unexpected at all, given our simulation exercise above.

Humans love to find patterns in small stretches of data when really there are none. Rory’s poor performance of late is not inconsistent with him still being the same player he’s been for the last few years. That is, he may still be pulling from the same distribution, with mean ~2.3 and sd ~2.7; maybe Rory just had a couple bad draws the last 2 weeks.

Or, maybe he has actually lost it (his putting does look awful). The point is that these last 2 weeks don’t tell us very much about which opinion is the correct one.