The United States Golf Association has a very simple formula for determining the most improved golfer for a specified period; typically a "season."
You will need your golfers' Handicap Index at the start date of the season as well as the end date of the season. To each player's start date Index add 12*. This is Value A. Similarly, add 12* to each golfer's end date Index. This is Value B.
Divide Value A by Value B and round to three decimal places. The resulting number is called the "improvement factor." The higher the improvement factor, the more a golfer has improved. The golfer with the highest improvement factor in your group is the most improved player.
|Starting Handicap Index||10.5|
|Ending Handicap Index||5.5|
|Value A||10.5 + 12 = 22.5|
|Value B||5.5 + 12 = 17.5|
|A ÷ B||22.5 ÷ 17.5 = 1.286|
|Starting Handicap Index||19.9|
|Ending Handicap Index||12.9|
|Value A||19.9 + 12 = 31.9|
|Value B||12.9 + 12 = 24.9|
|A ÷ B||31.9 ÷ 24.9 = 1.281|
In these two examples, Richard's Index improved by 5 strokes and Fred's by 7 strokes. Richard's improvement factor (1.286) is greater than Fred's improvement factor (1.281). Richard, therefore, improved more during the season. Between him and Fred, Richard would win the most improved golfer prize. This example shows that the improvement factor is different than a simple comparison of the starting and ending Indexes and shows that the person who has the largest net improvement in Index isn't necessarily the most improved golfer. Of course you will be comparing more than two golfers typically. You would be looking for who in your entire golf group had the largest improvement factor.
In a case where your group has 9-hole Handicap Indexes, you would add 6*, rather than 12*, to the Start Handicap Index and End Handicap Index.
* Dean Knuth, the main developer of the USGA's Course Rating and Slope Rating System, helped establish the formula for the most improved player. Adding 12 to the 18-hole Indexes and 6 to the 9-hole Indexes was determined to fairly reflect the level of improvement for players at various Index levels. Knuth is considered the world's top expert in handicapping and course rating. He was the Senior Director of Handicapping for the USGA from 1981 thorugh 1997.