Why is the SSA calculated for each round rather than using a fixed course rating like ball golf?
There’s no way to determine what an official SSA value would be for a course simply by taking measurements, looking at foliage, fairway widths and accounting for hazards. Not only that, it’s common for TDs to add temp holes, change tee or pin positions, or use new courses such that no SSA would be on file for that layout anyway. Using the scores of players with established ratings to produce an SSA has proven to be an accurate way to indicate how the course played that round. The only weakness of this system is that we require only 5 propagators to generate an SSA. Statisticians would prefer we use at least 30 propagators minimum for better accuracy. However, the PDGA has chosen 5 so that more players would get ratings. Some smaller divisions who play shorter layouts may not have very many propagators on a layout that round and would not get ratings in several events. The slightly higher inaccuracies produced with this system for individual rounds tend to even out over time. Plus, no round rating remains in an active player’s rating more than 12 months before it disappears.