Why It Should Be Six Factors Instead of Four Factors

Four Factors is a widely used basketball analysis framework developed by Dean Oliver. The four offensive factors are:

  1. Effective field goal percentage (eFG%).
  2. Turnover percentage (TOV%)
  3. Offensive rebounding percentage (OREB%)
  4. FT rate (FTM / FGA)

The four defensive factors are the same four factors for the opponents.

The basic idea of the Four Factors is to measure all possible outcomes of a ball possession. The results can then be used to assess why a team won or lost and where there is most room for improvement.

For example, if your eFG% is relatively good and TOV% relatively bad, it will probably be easier to improve your TOV%.

However, there are problems with the Four Factors. Two of the factors should be split in two. So, it should actually be Six Factors.

Problem with eFG%

In Four Factors, eFG% is used to measure the efficiency of field goal shooting. The equation for eFG% is:

This operationalisation mixes up two things: a player’s ability to hit FG shots and her ability to draw fouls on her FG shots.

Drawing fouls will raise a player’s eFG% That’s because if the shooter is fouled in the act of shooting, the shot counts as an FGA only if it goes in. In other words, when a shooter gets fouled she can only make her FGA – not miss it.

This mixing up damages the value of Four Factors for coaches. We want to analyse the team’s ability to hit FG shots separately from its ability to draw fouls. That’s because improving the two aspects calls for different practice methods.

So, eFG% needs to be split in two factors: 1) eFG% of FG shots where the shooter is not fouled in the act of shooting (clean eFG%), and 2) eFG% of FGS shots where the shooter is fouled in the act of shooting (foul eFGS%).

The two equations are:

  • (Clean FG + .5 x Clean 3P) / Clean FG shots = Clean eFG%
  • (Foul FG + .5 x Foul 3P) / Foul FG shots = Foul eFG%

Two problems with FT rate

Problem 1: Occurrences that are net negative for the team may cause FT rate to rise.

If the shooter misses a FG shot where he gets fouled it affects the FT rate more positively than if he gets fouled and makes the shot.

That is because: 1) A missed foul FG shot will not add to the number of FG attempts, but a made foul FG shot does, and 2) A missed foul FG shot provides the offense with two FTA, whereas a made foul FG shot will only provide one.

Problem 2: FT rate will not tell how they the team has done regarding the two basic aspects of free throws: earning FTA and making them. Hence they must have separate indicators.

This is hardly surprising since in 2007 Kubatko, Oliver, Pelton and Rosenbaum wrote: “This would imply Five Factors, but this one term [FT frequency] tends to capture the most important elements of both.”

To measure a team’s ability to hit FT’s there is no better tool than FT%.

To measure a team’s ability to earn FT’s I suggest this equation:

FT frequency = FT sets / Possessions

Six Faxtors

So, the Four Factors turned into Six Factors are:

  1. Clean eFG%
  2. Foul eFG%
  3. TOV%
  4. ORB%
  5. FT frequency (FT sets / Possessions)
  6. FT%

There are reasons why Dean Oliver designed the Four Factors to include four factors instead of six. The original Four Factors is an easy-to-implement concept since the factors can be calculated based on a traditional box score.

And as always, adding to the number of variables adds to the complexity of the analysis.

However, if one wants maximise the value of the factors for coaching, six is better four.

This blog is an edited combination of three blog published in 2014.

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