The slope rating of a golf course is a measure of its difficulty for bogey golfers. The term comes from the likelihood that when playing on more difficult courses, players' scores will rise more quickly than their handicaps would predict. The "slope rating" of a course thus predicts that rise. The term was invented by the United States Golf Association.
The USGA states that slope rating is a mark that indicates the measurement of the relative difficulty of a course for players who are not scratch golfers compared to the USGA course rating (e.g., compared to the difficulty of a course for scratch golfers). A slope rating is computed from the difference between the bogey rating and the USGA course rating. A golf course of standard playing difficulty has a slope rating of 113, and slope ratings range from a minimum of 55 (very easy) to a maximum of 155 (extremely difficult).
The USGA slope rating of a golf course is a mark that describes the measure of difficulty for a bogey golfer relative to a scratch golfer at a specific set of tees. It describes the fact that when playing on a more difficult course, the scores of higher-handicapped players will rise more quickly than those of lower handicapped golfers. The slope rating of a set of tees predicts the straight-line rise in anticipated score versus USGA course handicap, as in the mathematical slope of a graph.
A slope rating is calculated from the difference in a bogey course rating and a scratch course rating, more commonly known as the course rating. This difference is multiplied by 5.381 to get a men's slope rating or 4.240 to get a women's slope rating. Course ratings (bogey and scratch) are determined by course raters, who measure and record more than 460 numbers on a course rating form for each set of tees.
History of slope rating
In 1977, then Lt. Commander Dean Knuth, a graduate student at the Naval Postgraduate School, proposed an improved course rating system that involved numerical rating of ten characteristics for each hole. These ratings along with the weighted factors for each characteristic provided an adjustment to the distance rating for the course. The method used some elements of decision theory and was intended to be a systematic, quantitative approach to course rating. It was the basis for the present USGA Course Rating System. When he was stationed in Norfolk, Virginia, he developed a method for Bogey Rating. Together, the Bogey Rating and the Course Rating produces the Slope Rating of a golf course. Knuth served as the USGA's Senior Director of Handicapping for 16 years, beginning in 1981.
In 1982, the Colorado Golf Association rated all of its courses using the new procedure, under the leadership of HRT member Dr. Byron Williamson. In 1983, Colorado tested the Slope System with positive results. Five other states joined Colorado in the test during 1984, and others followed in subsequent years. Since January 1, 1990, every golf association in the United States that rates golf courses uses the USGA Course Rating System. As of 1994, foreign golf associations licensed to use the system were: Scotland, Canada, Ireland, Wales, Sweden, Denmark, Germany, France, Bermuda, the Republic of China, Costa Rica, France, Hong Kong, India, Jamaica, Korea, Malaysia, Mexico, the Netherlands, Indonesia, Singapore, and the Philippines. Australia is the latest country to adopt the Slope System of course rating. It has continued to grow in use worldwide. The possibility of a common worldwide use of the USGA Course Rating and Slope Rating system is being discussed as interest grows in 2011.