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The Four Factors

Ever since I stumbled across Dean Oliver's Journal of Basketball Studies a few months ago, I've been tracking some of his statistics during the college basketball season. A few of those statistics include the Four Factors. If you want more in-depth discussion of these numbers, Oliver's site offers plenty. I'm going to summarize them as best I can here.

In the most basic sense, the Four Factors are the ingredients for success on the court. The factors are: shooting, turnovers, rebounding, and reaching the foul line. They are basic aspects of the game that have an obvious correlation to winning and losing. By looking at them in a certain way, Oliver hopes to gain greater insight into what teams do well and what they don't--and what it all means.

Some factors are more important than others. Specifically, shooting is the most important factor. In order of importance:

1) Effective (or adjusted) FG%
2) Turnover Rate
3) Offensive Rebounding Rate
4) FTA/FGA; FTM/FGA

About each factor:

Effective Field Goal Percentage (shooting) is defined as:

eFG = [FGM + (0.5 x 3PM)] / FGA

This is a simple adjustment that compensates for three-pointers. Because of the adjustment, you will see higher numbers on average than you will with regular FG%.

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Turnovers per Possession (or Turnover Rate), as you might imagine, is:

Turnovers / Possessions

Possessions aren't tracked in any basketball box score, so they have to be estimated. Oliver estimates them this way:

Possessions = FGA - OReb + Turnovers + (0.475 x FTA)

[Actually, Oliver uses 0.4 as the multiplier for FTs. Ken Pomeroy has discovered that 0.475 works better for the college game. Oliver works with NBA data.]

The 0.475 is used to adjust for free throws--it's an attempt to estimate how many possessions an average free throw attempt (FTAs occur in varying situations, so it makes this estimation difficult) is worth.

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Offensive Rebounding Percentage (or Offensive Rebounding Rate) is:

OR% = Off Rebs / (Off Rebs + Opponent's Def Rebs)

This measures how well a team converts opportunities for offensive rebounds. Teams that play at a faster pace will have more possessions and take more shots, thus creating more opportunities for rebounds. For this reason, comparing raw rebounding numbers can sometimes be misleading.

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For measuring how well a team reaches the free throw line, there a couple of different ratios to look at:

FTA/FGA as well as FTM/FGA

Both offer insight into how effectively a team uses the free throw line.