The Quirks of the Slope

We will sometimes choose some of the more interesting questions asked by our members to share with you. Our most recent one comes from a member who shot a 70 on a course with a rating of 71.3 and slope of 132 (something we can all aspire to). When entering his score into MyScorecard, the differential read -1.1, which was actually less than the -1.3 the difference between the score (70) and course rating (71.3). Wouldn’t you expect that if you played a harder course, it should be greater than the difference of the rating and score?

It’s a great question, and an issue that has tripped up a number of folks out there The result is counterintuitive, but it is correct. The calculation for the differential is (score – rating) * 113 / slope. Thus, for harder courses, a positive differential is lowered and a negative differential is raised (i.e. they both get closer to zero).

The calculation makes intuitive sense for a positive differential. If you play a harder course, you played “better” than your score would suggest, and thus your differential (adjusted score) should be lower. So a score of 90 on a course with rating/slope of 70/113 would lead to a differential of 20 while the same score on a course with a rating/slope of 70/135 would lead to a differential of 16.7 (a better adjusted score).

Using the same logic leads to a question mark when the differential is negative. Shooting a 68 on the same courses leads to a differential of -2 on the easy course, but only -1.7 on the harder course. Something seems to be backwards!


So what’s happening?

A better way to think about it is how the differentials are used to calculate a course handicap. The index (i.e. a modified average of the differential) is multiplied by the slope/113 to get to the course handicap. The difference in course handicaps is how many strokes a player receives. Thus, on a hard course two players with average differentials of 10 and 20 may see their course handicap both rise to 12 and 24, and the difference being 12 strokes (an increase of 2 strokes). However,, a player with average differential of -2 vs a player would see their handicap decrease down to -3, creating a difference of 5 strokes vs. the 20 handicap player. Thus, even though the movement of the differentials seems counter-intuitive, the ultimate result – the difference in strokes given between players – remains consistent.

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