Strokes gained is a golf stat created by Mark Broadie, a professor at the Graduate School of Business at Columbia University. He is a business professor but also an avid golf player who though he could use data to analyze a golf player's game. Broadie had access to ShotLink data from the PGA Tour, which is a "collection and analysis of shot-by-shot data during competition play" and used it to develop the strokes gained metric
The definition on the PGA tour website is "Strokes gained is a better method for measuring performance because it compares a player’s performance to the rest of the field and because it can isolate individual aspects of the game."
This means we can compare each and every shot you take with a benchmark, which is normally the PGA Tour (where we have Shotlink tracking each and every shot, which means we have tons of data). This will allow you to know how good or bad each of your shots was, which will be very helpful to know where you need to improve.
The basic data used is the average number of strokes needed to hole out from every distance and location (tee, fairway, rough, sand) on the course, also called the strokes-to-hole. For example, the PGA Tour's scoring average (also known as the baseline or the benchmark) for a ball lying on the fairway and 116 yards from the hole is 2.825 shots.
To calculate the strokes gained for a given shot, we calculate the difference between the benchmark from the starting position and the benchmark from the finishing position, minus one to take into account the shot.
To calculate the strokes gained for a given shot you just have to do the following:
Strokes Gained for shot = Starting position Benchmark - Finishing position Benchmark - 1
Let's imagine you are playing a 446 yards par-4. The PGA Tour's scoring average, or benchmark, for a shot from 446 yards from the tee (remember, distance and location) is 4.1 shots.
You hit a great drive and leave the ball in the fairway 116 yards from the hole. We go the benchmark again and we find that in the PGA Tour the scoring average from 116 yards on the fairway is 2.825.
How good was your drive? From the tee, your scoring average was 4.1, but after the first shot you were in a position where the scoring average was 2.825. If you subtract those numbers, you get 4.1 - 2.825 - 1 = 0.275, which means you "gained" 0.275 shots, a great drive!
Your second shot takes the ball to 16' 11" on the green, which means you go from a benchmark of 2.825 shots to 1.826 shots, your strokes gained is 2.825 - 1.826 - 1 = -0.001, which means that was just like the average shot in the PGA Tour.
The average score from 16' 11" on the green is 1.826, but you hole the putt, which means you strokes gained for this shot were 1.826 - 0 - 1 = +0.826, a great putt for birdie!
If you want to calculate the strokes gained for different lies and distances we have created a strokes gained calculator, have fun with it!
Calculating the strokes gained for each shot can be helpful, but the real breakthrough comes when you group your shots by type (ie driving, long approach, short approach, around the green, long putts, short putts) and get your "strokes gained" for each group. That will tell you exactly your strengths and weaknesses and you will know where to focus your training to become a better golfer.