Advanced Metrics Handbook, Vol. 1: Effective Field Goal Percentage

Orlando PInstriped Post Photo / Bruce Maddox

Part of an occasional series explaining some of the advanced statistical terms employed at Orlando Pinstriped Post. Today's topic: effective field goal percentage, or eFG% for short.

On November 4th, 2009, Orlando Magic forward Mickael Pietrus scored 15 points in a victory over the Phoenix Suns, but shot just 4-of-10 from the floor, for 40%. Conventional analysis would hold that 40% shooting isn't acceptable at the NBA level, but it'd be a bit misguided. Traditional field goal percentage doesn't really tell the whole story, which is why former L.A. Clippers head coach Mike Dunleavy developed eFG%, a better measure of shooting proficiency, during his playing days in the early 1980s.

The formula:

(FG + 0.5 * 3P) / FGA

In plain English:

Dunleavy believed that shooting percentages should reflect the fact that three-point shots are worth more than two-point shots. eFG% accomplishes this task by multiplying the number of three-pointers made by 1.5

What it's for:

Evaluating volume three-point shooters, like Pietrus, whom traditional FG% underrates. For his career, Pietrus has shot 43.5% from the field. However, Pietrus' tendency to let fly from beyond the arc--46.2% of his shots come from long range--boosts his eFG% to 51.8%. In contrast, it won't tell you anything new about Magic center Dwight Howard, who's made just one three-pointer in his six-year career.

The takeaway:

Pietrus indeed shot 40% in Orlando's win against Phoenix, but looking at the bigger picture, you'll see he was more efficient than what raw FG% indicates. Three of his four field goals came from beyond the arc. Plugging his numbers from that game into the formula, we see that Pietrus registered an eFG% of 55.0%, which is slightly higher than his season average o 54.0%.

Additionally, eFG% is a proven measure of team success, as the noted statistician Dean Oliver identified it as one of the four factors of winning in his book Basketball On Paper. It's not a novelty or a curiosity, in other words. It's a relevant, respected component of modern basketball analysis, though it's not even the best advanced shooting metric available, as we'll see in a later installment in this series.

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