Monday, August 01, 2005

Four Factors

The offensive and defensive summary pages are based on Dean Oliver’s four factors concept. You can read Dean’s more detailed explanation of the four factors here. Essentially, the four factors are the building blocks to the efficiency formula.

Efficiency data gives you an idea of the quality of a team’s offense or defense, but the four factors tell you why a team is good or bad when they have or don’t have the ball. Here’s a breakdown of how each statistic on this page is calculated…

Effective field goal percentage is like regular field goal percentage except that it gives 50% more credit for made three-pointers.

eFG%  = (.5*3FGM + FGM) / FGA

Turnover percentage is a pace-independent measure of ball security.

TO% = TO / Possessions

Offensive rebounding percentage is a measure of the possible rebounds that are gathered by the offense.

OR% = OR / (OR + DRopp)

Keep in mind that rebounding percentage is computed from box score data which does not contain team rebounds. Therefore, the figures shown here may differ slightly from calculations made on the rebounding totals provided by a school.

Finally, free throw rate captures a team’s ability to score from the line.

FTRateoff = FTM / FGA
FTRatedef = FTA / FGA

Defensive FTRate uses FTA in the numerator since the defense has little control on the percentage of free throw attempts made by the opposition.

In Dean’s piece, he mentions the relative importance of each factor. In the NBA, eFG% is easily the most important factor, followed by TO%, OR%, and FTRate. A “RoboScout”-type analysis of games from the 2005 season shows that the importance of each factor is similar in college, with free throw rate being slightly more important in the college game, but still taking a back seat to offensive rebounding. Each team is different though. For instance, Gonzaga’s free throw rate was the second most important contributor to their offensive success. For Michigan State, offensive rebounding ranked second.