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%.
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.
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.
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.