A golf score reflects a golfer's skill and experience. Course difficulty also plays a significant role. Even golfers of equal ability may post lower scores on some courses, while other courses can be utterly demoralizing.
The LPGA Tour Ford Championship, which concluded on May 30 (Korea time), resembled a birdie party. Winner Kim Hyo-joo fired 11-under-par 61 in both the first and third rounds, finishing with a four-day total of 28-under par. Runner-up Nelly Korda of the United States posted 26-under par. The venue, Whirlwind Golf Club in Phoenix, Arizona (par 72, 6,675 yards), allowed 49 of the 76 players who made the cut to post double-digit under-par scores. Even the last-place finisher recorded an under-par score of 1-under. Balls landing on the firm fairways rolled considerable distances. By contrast, the U.S. Open — often called a "war against the course" — has produced over-par winners.
Can such subjective course difficulty be quantified? The tool for measuring course difficulty is the "course rating" system. Searching a golf course name on Korean portal sites may show a "Korea Golf Association Course Rating Certification" label. Courses that have not been certified carry no such label.
What exactly does a course rating mean? Simply put, a course rating indicates how difficult a course is for a scratch golfer with a handicap of zero. If a scorecard or course map shows a course rating of 72.3, it means a scratch golfer is expected to average 72.3 strokes on that course under normal course and weather conditions.
There is also something called a "slope rating." This concept is somewhat harder to understand because it accounts for relative difficulty based on handicap. It introduces the concept of a "bogey rating." While the course rating is based on a scratch golfer, the bogey rating measures course difficulty for a bogey golfer. The slope rating represents the difference between the course rating and the bogey rating. Higher-handicap golfers may see their scores rise sharply due to increased course length, long rough, and deep bunkers — and this is where the slope rating plays a crucial role. Some people mistakenly think the word "slope" refers to a correlation between course gradient and difficulty. In fact, slope refers to the gradient of the line connecting the course rating and bogey rating values on a graph. A higher slope rating value means the course is more difficult for higher-handicap golfers.
Calculating course ratings and slope ratings requires expert judgment and considerable mathematical computation. The experts are typically evaluators from regional golf associations. In Korea, the Korea Golf Association handles certification. Following the course rating manuals of the United States Golf Association (USGA) and the R&A, evaluators conduct on-site inspections of every corner of a course to assess difficulty. Recently, digital data such as Google Maps has been used to create preliminary documentation of course layouts and obstacles, which is then refined through field visits.
Several factors are considered when calculating course difficulty. Length is the most important. Length calculations also account for roll, average wind speed in the area, dogleg shapes, and elevation changes. Additional difficulty values are assigned to on-course obstacles including bunkers, trees, terrain, out-of-bounds areas, fairway width, water (penalty areas), and rough.
