Golf is a club-and-ball sport in which players use various clubs to hit balls into a series of holes on a golf course in as few strokes as possible. Each player drives a golf ball off a wooden tee at the start and eventually putts the ball on a soft grass surface into a hole. In golf, you are at a considerable advantage if you can drive the golf ball far. As professional golfers gain more experience and technology continues to improve, it makes sense to assume that professional golfers are driving the ball farther year after year. To test this theory, researchers set out to see if professional golfers are driving the golf ball noticeably further than they were three years prior. Data were collected from 111 male professional golf players. Their average driving distances off the tee (in yards) in 2015 and in 2018 were recorded, and the changes in their average driving distances from 2015 to 2018 were calculated (using order of subtraction 2018 - 2015). Call the change in average driving distance from 2015 to 2018 each player's "improvement score