Effective Field Goal Percentage or Field Goal Percentage: Better Predictor of Success?

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To see which statistic was a better predictor of regular season success, I ranked every team’s record, effective field goal percentage, and field goal percentage in their conference and the NBA, as a whole, in each of the past 5 seasons.  After that, I found the average difference between a team’s ranking for their record and effective field goal percentage and between a team’s record and field goal percentage.

Within the conference, the average difference between a team’s ranking for their record and effective field goal percentage was 2.64 spots, while it was 2.80 spots between a team’s record and field goal percentage.

Within the whole NBA, the average difference between a team’s ranking for their record and effective field goal percentage was 4.89 spots, while it was 5.55 spots between a team’s record and field goal percentage.

Overall, both statistics are pretty good determinants of the success of the team, but, while it may be a relatively minute difference, it is clear that effective field goal percentage is a slightly better predictor for a team’s regular season success.  There were a few outliers for each statistic where the difference between a team’s rank for their record and either effective or regular field goal percentage was at least 6 spots in their conference and at least 10-12 spots in the NBA, as a whole, but for the most part both statistics were more closely related to a team’s ranking for their record than the averages would lead one to believe.

As for the postseason, I went through every game this postseason and calculated the effective field goal percentage and field goal percentage for each team as an overall series total and individual game total.

Using effective field goal percentage, 4 series were won by the team with the lower series total (New York over Boston, Indiana over Atlanta, Memphis over Los Angeles Clippers, and Memphis over Oklahoma City).  There were also 17 games (~20%) that were won by the team with the lower effective field goal percentage.

This can happen because effective field goal percentage does not take into account points from free throws and the fact that teams who take more shots will usually have more field goals made, even if it is at a lower field goal percentage than their opponent.  In the 17 games where the team with the lower effective field goal percentage won, the winning team, on average, attempted 6 more shots, 8 more free throws, and made 10 more free throws than their opponent.

For field goal percentage, 4 series were also won by the team with the lower series total (New York over Boston, Indiana over Atlanta, Memphis over Los Angeles Clippers, and Miami over Indiana).  There were also 18 games (~21%) that were won by the team with the lower field goal percentage.

This occurs for the same reason as with effective field goal percentage, except 3-point field goals are an added variable.  For instance, if a team has a field goal percentage of 45% (9-20) with 4 3-pointers, that is 22 points. If their opponent has a field goal percentage of 50% (10-20) but makes only 1 3-pointer, that is 21 points.

Overall, effective field goal percentage, in the regular season and postseason, is a slightly better predictor of success than regular field goal percentage.  Effective field goal percentage is better only because it takes out 3-point shooting as another variable in how a team scores their points.

This is because effective field goal percentage puts both teams’ field goal percentage in terms of the 2-point field goal percentage needed to score the same number of points.  The only way to beat a team while shooting a lower effective field goal percentage is to make more free throws and attempt more shots, which are either caused by having fewer turnovers or more offensive rebounds than your opponent.

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Jacob Rubel is a senior at the University of North Carolina at Chapel Hill majoring in Exercise and Sports Administration with minors in Music and Statistics.  Additionally, Jacob was a participant of the 2012 Manhattan Sports Business Academy.  He also writes for sportsbusinessu.comspitballingstats.com, and his personal blog killerstatz.com.

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