Golf Analytics

How Golfers Win

Measuring Consistency

Consistency is often talked about in golf – by golfers themselves, by the media, and by fans – but it’s one of those undefined words that can be used in any desired way to get your point across. What I’m going to talk about today is week-to-week consistency of performance.

First, we need to set a baseline for performance to compare a player’s week-by-week play too. Finishing top 10 in an event represents a very positive performance for a Tour average player, but much closer to expectations for world #1. At 15th Club we use Performance Index to benchmark what we expect in a particular week from each player. For example, this week at the WGC Bridgestone we expect Dustin Johnson and Justin Rose to be the best performers and Kevin Na to be close to the middle of the pack.

With Performance Index shown in strokes versus the field, that’s the metric of choice for measuring performance. The truly elite performances in the last two seasons have been events like Brooks Koepka’s first US Open, Hideki Matsuyama at the Bridgestone, and Molinari at Quicken Loans. These are in excess of 5+ strokes versus the field per round.

With measures of performance and expectation established, it’s as simple as measuring how each player at each event measures up over 2017 and 2018. For example, Dustin Johnson had a low of about -5 strokes versus expected per round at the 2017 Memorial and a high of about +3 strokes versus expected per round at the 2018 Tournament of Champions. On the graphs later, I’ve chosen to show this measure as strokes per two rounds to show two round and four round events on the same level.

Measured this way performance is skewed with a longer left tail – in other words a player’s poor events will be further from 0 than his best events. There could be many reasons for this from injury, the effects of pressure when playing well, the tee-time effect (players playing well on the weekend play in the typically tougher afternoon), less motivation if far from the lead, and other more esoteric reasons behind how performance is judged. The average event for top-level players is about -0.5 strokes versus expected per two rounds.

10th percentile performance is roughly -5 strokes versus expected per two rounds and 90th percentile performance is roughly +3 strokes versus expected per two rounds. An elite player with a 10th percentile performance will very likely miss the cut, while an average player with a 90th percentile performance will have a great chance at a top 20.

To measure consistency, I’m taking the average absolute difference between actual and expected performance (difference from zero) of every event a golfer has played since the start of 2017. These range from about 1.6 strokes versus expected per two rounds for the most consistent to 5.0 strokes versus expected per two rounds for the least consistent. In other words, if the expected score for the most consistent player is 140 over two rounds, on average the difference between their actual score and 140 will be 1.6 strokes better or worse.

More consistent players in 2017-18

Less consistent players over 2017-18

Both lists have a range of players, with the less consistent featuring some guys like Kaufman and Willett who have struggled over the last two years along with guys like Landry and Mitchell who have played well. Same for the consistent list, Casey is one of the best in the world, while most are in the 100th to 250th best in the world zone.

Along with actually measuring consistency, it’s critical to discuss why it matters. Elite players whose games are very consistent will give themselves fewer opportunities to win than otherwise expected. At the same time, weaker players whose games are very inconsistent will win and be in contention often, but will also no-show most weeks. In a world where everything from your media/fan legacy to World Rankings to prize money is based largely on heavily rewarding victories, both of these facts skew how players are viewed.

I’ll close with a few notable players:

Justin Rose
Justin Rose-consistencyRose has managed to avoid any genuinely poor events with his worst being a T63 at the Bridgestone last year where he was 8 back after 36 holes and had a lackluster weekend. On the other hand, he’s had eight extreme over-performing events of which he’s won four and lost in a playoff in another.

Paul Casey
Paul Casey-consistency
An average player would be expected to have 7 extreme good or poor events in 37 events, but Casey has had only three – two of them being his only missed cuts and the third being his 6th at the 2017 Masters. Casey ranks as one of the best performing golfers in the world over 2017-18, but has struggled to generate the kind of winning performances his peers do.

Jon Rahm
Jon Rahm-consistency
Rahm has a reputation as a volatile player and that’s borne out here. He’s had more extreme events than expected, but mostly skewed towards the positive. He has made his poor events notable with the 2017 & 2018 US Opens and nearly the 2018 Open appearing among his low-lights.

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