In the USGA Handicap System, the method for stroke allocation required collecting hole-by-hole scores from a large group of players in two groups of players, group A (low handicap players) and group B (high handicap players). For match play allocation, the difference between these groups was compared and, for stroke play, the combination of the groups was compared against par.
In theory, this method provides reliable results for stroke allocation, but in practice it often produced inconsistent and questionable results. The most common issue was a lack of players to form the specified groups (A and B) who also played from the same tee. The low handicap players would often play the longer tees, and the higher handicap players would often play a shorter set of tees.
For women, it was often a challenge to find enough low handicap players to make a meaningful group A, so the comparison was often made between mid-handicap players and high handicap players.
There was a second method available that used regression and did not require players to be only in groups A or B, but to work it needed a large spread of handicaps with scores from the same set of tees. When looking at a common tee, scores collected were often from players of similar handicaps, not creating enough spread to get a good analysis.
Additionally, the results could change each time it was run, as a different group of players was used, the range of handicaps used was different, or even the time of year might impact the scores from certain types of players (a wet spring might impact high handicap players much more than low handicap players).
For clubs that did not have a lot of players in the desired handicap range, or enough regular players with a Handicap Index® (e.g., a golf resort), it was often difficult to produce any stroke index tables with confidence using the previous methods.
From both USGA and worldwide research, in match play, the stroke index order is not important in producing equitable results if the strokes are spread out, consecutive low strokes are avoided, and low strokes at the beginning or end of each nine are avoided. So, applying the triad concept of using three-hole clusters (with the lowest stroke hole on each nine in the middle of the nine), spreading out low stroke holes, and avoiding consecutive low stroke holes produces a simple but effective method for allocation.
As stroke index values are also used in stroke play or Stableford play, it was important to generate a raw ranking based on overall difficulty, which is where the Course Rating data is used. Using Course Rating data, which factors in both effective playing length and obstacle ratings, provides a consistent method regardless of the makeup of players at the course.
While the stroke index values are ultimately adjusted to accommodate the recommended procedures for match play, they are generally consistent with the order of difficulty as ranked using Course Rating data. Since the maximum hole score allowed for handicap purposes is based on a net double bogey, which is tied to the stroke index value, it is important to have the holes ranked in a general order of difficulty.
As with the previous USGA Handicap System, stroke index allocation is a recommendation and courses are free to use whichever method they choose. There is no recommendation for a course to run a new allocation solely due to the move to the WHS. However, for courses that are looking to run a new allocation, the new WHS method produces consistent and acceptable values without the need to find specific players and collect hundreds of scores from a common tee.