Get To Know An Advanced Stat: Effective Field Goal Percentage & True Shooting Percentage
In last week's debut of our 'Get To Know An Advanced Stat' series, I explained why using possession based ratings is much more accurate in evaluating team offense and defense than raw points or field goal percentage is.
This week, I'll look at how the way we evaluate the shooting/scoring performance of individual players has changed as well.
The most basic way of judging how a player shot the ball and scored the ball on any given night or over a selected period of time is with simple field goal percentage. It makes sense - simply look at how many shots a player has made versus how many he has taken and missed.
The problem with that basic way of thinking, though, is that it's both unfair and unrealistic to compare the field goal percentages of a player like Stephen Curry, who takes over seven three-pointers per game, and a player like say, Andre Drummond, who literally doesn't shoot from outside the paint. For this reason, Effective Field Goal Percentage is used.
Effective field goal percentage takes regular field goal percentage and adjusts for the fact that three-pointers are worth 50 percent more than two-point field goals - EFG% = (FGM + (0.5 x 3PTM)) / FGA. So using Curry as the example, last season Steph finished with a field goal percentage of 45.1, which is right about league average, even though we know he's far, far better than a league average shooter (I assure you, 'greatest ever' is better than average). When you weight that for the added value of a three-pointer, however, Curry's effective field goal percentage of .549 ranked 15th in the NBA, much more indicative of his elite status.
DeAndre Jordan, on the other hand, led the league in both field goal percentage and effective field goal percentage, but the difference is that for him, there is no difference between the numbers. Jordan's .643 EFG% is the exact same as his 64.3 FG%, because he didn't take any three-point attempts last year.
And then there's True Shooting Percentage, which is probably the best measure of how a player scored and shot the ball from an efficiency/possession standpoint, because it also takes free throws into account (see the formula here). As you may recall from last week, a possession doesn't officially end until possession of the ball switches hands, so just as teams can salvage their efficiency (per possession) on a poor shooting night by getting to the charity stripe, so can players (something lost on Rudy Gay, who only got to the line four times despite his 11-of-37 performance on Monday).
With that in mind, think of James Harden, who scored 25.9 points per game last season on a slightly below field goal percentage of 44.3 and a slightly above average effective field goal percentage of .504. Look at those numbers and you'd assume Harden scored a ton on pretty average efficiency, but definitely not great efficiency, right? But factor in Harden's league leading 792 free throw attempts and his 674 made free throws in 2012-13, and then you get an idea of just how eye popping 'The Beard' was from an efficiency standpoint, as his 25.9 points per game actually came on a True Shooting Percentage of .600 (good for 14th in the league), where the league average is usually around .530.
The basic premise here is pretty simple - If it's better and smarter to evaluate team efficiency based on how teams score per possession as opposed to their raw number of points without context, then it's also smarter to evaluate a player's scoring efficiency using a more possession oriented shooting metric, and True Shooting Percentage is just that.
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