What do the numbers mean?
Which golf course is more difficult?
Course A: 71.3/121
Course B: 69.2/132
Easy... at every handicap level, the answer is Course A!
Surprised? Many, if not most golfers probably would have guessed Course B. It just goes to illustrate the many myths and misunderstandings that abound regarding the subject of Slope.
MYTH No. 1
Slope is the major indicator of the difficulty or, to put it another way the higher the Slope, the more difficult the course. Wrong! As the above example confirms, it is the Course Rating and not the Slope which is the more dominant factor defining course difficulty.
As each score a golfer posts is broken down into a numeric value known as a "differential," it is the Course Rating that is the more important factor in the calculation (Adjusted Score minus Course Rating multiplied by 113 divided by Slope Rating).
To put the Course Rating vs. Slope Rating debate into perspective, it takes more than 20 units of Slope to have the same impact as a single stroke of Course Rating on a 5-handicapper. As a golfer's handicap increases, this ratio of the importance of the two values changes, but even for a 20-handicapper it takes five to six points of slope to have the same impact as one stroke in the Course Rating.
MYTH No. 1A
Two Courses with the same Slope are of equal difficulty.
Wrong! A course with a rating of 71.5/125 is about two strokes more difficult than a course with a rating of 69.6/125 at every handicap level.
MYTH No. 2
Slope rating can be compared from one course to another.
Wrong! There is nothing more dangerous than trying to draw any sort of meaningful conclusions by comparing Slope Rating from one course to another.
So, What is Slope?
Slope merely tells how "proportionately" more difficult a golf course (by tee set up) plays for higher handicapped golfers as opposed to lower handicapped golfers. The more difficult the play proportionally for the higher handicappers, the greater the Slope.
That's it! Slope doesn't tell you how the course proportionally plays from any other set of tees, let alone tell you how it compares with other courses.
This proportionate difficulty is measured via a course rating process that evaluates each hole and each shot through the eyes of a scratch golfer and bogey golfer. This process is so thorough that an actual rating for how the scratch and the bogey golfer is computed and it is the gap between the Scratch and Bogey rating that determines the Slope.
For example a set of tees may be issued a Course or Scratch rating of 71.0 and a Bogey Rating of 92.0. What this means is that if a scratch golfer were to complete 20 rounds, we would expect his 10 best scores to average around 70.5. If a golfer with a handicap index of 20.0 were to complete 20 rounds, we would expect his ten best scores to average around 92.0. Based upon this gap of 23.8 strokes between the two ratings (92 - 71= 21), a Men's Slope Rating of 113 would be issued (difference in ratings times 5.381). *A constant of 5.381 is achieved by finding the slope of a line between 71.0 and 92.0. These are the scratch and bogey ratings of the USGA standard course with a rating of 71.0/113.
The Scratch and Bogey ratings are somewhat volatile, and when a series of factors or obstacles on a course tend to effect one of the two golfers, then things will happen to the Slope.
For example, if a set of tees has a high number of holes that the bogey golfer can reach the green in "regulation," an upward pressure on the Slope will be exerted. Think about it … on most of these holes the bogey golfer is approaching the green with a long iron or a fairway wood, while the scratch golfer has a wedge or less in his/her hands. Clearly the bogey golfer is much more susceptible to any of the greenside trouble present on the holes (bunkers, difficult chips, etc.) … the kind of trouble which can cause scores to soar. Such a scenario will force the bogey rating higher, widen the gap between the two ratings and result in a higher Slope. Now consider a set of tees, even on the same course, where most of the holes are unreachable in regulation for the bogey golfer. Now it is the scratch golfer who has the longer approach shots, perhaps with mid to long irons, while the bogey golfer may merely be chipping/pitching to the green in one over regulation. To a certain degree, the tide of proportionate difficulty has turned. Though both ratings will be increased because of the added length of these tees, the gap between the Scratch and Bogey ratings may be staying relatively constant or may widen at a very slow rate.
These upward and downward pressures help explain why a Slope rating may increase sharply at a course from the Forward tees to the Middle tees (Bogey rating as the approach shot become longer), yet hardly change from Middle to Back (gap increasing slowly due to shorter approach shots of the bogey golfer). It also explains how a shorter course can be issued a Slope that may seem to be a little high, or how a longer course may be issued a Slope that may seem to be a little low.
Another factor that can greatly impact the Slope is forced lay-ups. If the Scratch golfer is forced to lay-up on a hole because of any one of a number of obstacles (water hazard, severe dogleg, etc.), this will increase the Scratch rating. That's because of the extra yardage of the approach shot. It will leave the Bogey rating untouched. This higher Scratch rating narrows the gap with the Bogey rating and decrease the Slope. Conversely, if the forced lay-ups only affect higher handicappers, the Bogey rating and Slope will increase.
The Golf Association of Philadelphia along with many other USGA associations have found these myths to be wide spread. These excerpts were taken from an article written by staff from the Northern California Golf Association.