Measuring McIlroy's Performance

For those of you who had the chance to watch the recent U.S. Open at Congressional Country Club in Bethesda, Md., you saw Rory McIlroy turn in one of the more dominating performances in major championship history. But how dominant was it?

After Congressional CC made some course alterations in advance of the U.S. Open, the Maryland State Golf Association re-rated the course in November of 2010, accounting for new tee sets and the other changes to the course. The course rating from the U.S. Open tees was 76.8, with a slope rating of 141. That rating is likely lower than the course actually played during the event, due to increased rough height and other obstacles. In addition, the USGA sometimes moves tees around during the four rounds of the event, which would also slightly change the yardage of the course and therefore would constitute a change in the course rating. But for the purposes of this blog post, let’s look at McIlroy’s four rounds and see what his handicap differentials were, using the 76.8/141 rating that the MSGA produced last year.

Round 1 – 65 – Handicap differential is -9.5
Round 2 – 66 – Handicap differential is -8.7
Round 3 – 68 – Handicap differential is -7.1
Round 4 – 69 – Handicap differential is -6.3

In the USGA handicap system, you need at least five scores to have a valid handicap index. And even with just five scores, the formula would only look at the lowest differential, which in this case is -9.5. So if we computed a handicap index for McIlroy based on these scores, and we took his lowest differential, his course handicap for a future round at Congressional would be a whopping +12. Anyone out there in GAP land feel like competing against that?

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