Strokes Gained can be best described as progress to the hole, measured in strokes, rather than yards or meters.
Invented by Columbia University professor Mark Broadie, utilising the PGA Tour's ShotLink data, Broadie was able to calculate how many shots, on average a player had remaining to the hole from every distance.
Strokes Gained allows us to look at every shot taken during a round, and to compare it to a benchmark.
Players who underperformed to the average displayed negative Strokes Gained, whereas a player who beat the average, gained strokes.
This means that for every shot a player hits we can assign that shot a score showing how many strokes the player gained or lost compared to the average of their peer group/benchmark, hit that same shot. This level of granularity allows us to answer questions about players' performance that traditional metrics do not.
Example
Let’s consider a player who hits the green from the tee on a par 3 and then holes the putt for a birdie.
Traditional stats will tell us that the player made the green in regulation and then 1 putted to achieve a birdie. However, this doesn’t tell the full story. The player may have just made it on the green and then holed a 40-foot putt or they may have hit their tee shot right next to the pin for a tap in. With strokes gained, we can analyse each shot individually.
So let’s say the hole is a 200-yard par 3, the strokes gained model tells us that on average scratch player will take 3.37 shots to get down from this distance. Let's say the player hits the ball to 3 feet, we know that the average scratch player will take 1.08 shots to get down from here. We can now calculate how many strokes the player took off of their expected amount to complete the hole from that one swing of the club:
Strokes Gained = (Expected shots to complete hole before the shot) - (Expected shots to complete the hole after the shot) - 1 (for the shot itself)
So we can assign the tee shot a strokes gained value of 3.37-1.08-1 = 1.29 and the putt and strokes gained value of 1.08-0-1 = 0.08. So by looking at it through the strokes gained lens we assign the majority of the credit for making the birdie to the tee shot (that one swing of the club gained the player a hole 1.29 shots against the average scratch player).
Now that we can score every shot in this fashion we can look at the cumulative score of different categories and distance bandings of shots to analyse their overall performance on those types of shots.