Five Factors – or Improving the Validity of Four Factors

Four Factors, developed by Dean Oliver, is a widespread concept in basketball performance analysis. Yet there is a serious flaw in it: it uses eFG% to measure the efficiency of field goal shooting. This is an invalid procedure, as shown here.

What then would be a valid indicator for the efficiency of field goal shooting within the framework of Four Factors?

Actually, two indicators are needed: eFG% of FG shots where the shooter is not fouled in the act of shooting (clean eFG%) and eFG% of FGS shots where the shooter is fouled in the act of shooting (foul eFGS%). This is the most useful way of including all FG shots  in the analysis – even those shots where the shooter is fouled and misses the shot.

The equations are:

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

Adding to the number of variables adds to the complexity of the analysis. However, the practical value of the analysis is also improved since now getting to the free throw line and hitting FG shots are measured as separate issues. At this point Four Factors have turned into Five Factors:

  1. Clean effective field goal percentage
  2. Foul effective field goal percentage
  3. Turnovers per possession
  4. Offensive rebounding percentage
  5. Free throw frequency

However, Five Factors will eventually become Six Factors, since there is a practical and theoretical problem with the factor of free throw frequency.

2 thoughts on “Five Factors – or Improving the Validity of Four Factors

  1. On Twitter @DeanO_Lytics or Dean Oliver commented this entry: “This overcomplicates it. Fouls on shots aren’t that common. All factors can be broken down, but keep it at 4.”

    “Fouls on shot on are not that common.”: In fact they are quite common for close-range FG shots. In the sample of my dissertation (22 games in the Finnish league games) 11% of all FG shots led to a shooting foul. Fouls were divided very unevenly. For close-range 2-pointers the foul percentage was 20%, for other types of FG shots close to non-existent.

    So, ignoring shooting fouls when measuring FG shooting efficiency makes it impossible to validly compare the efficiency of different types of shots – and consequently to validly compare the FG shooting efficiency of different players. Especially comparing close-range shooting efficiency of different players using eFG% is misleading.

    “This overcomplicates it.” & “keep it at 4”: Or maybe it’s rather that keeping the number of factors at 4 complicates interpreting the results?

    As shown, eFG% can not be the 4th factor or the one to validly measure FG shooting efficiency. eFG% could be replaced by “Total eFGS%” that would also include the FG shots ignored by eFG% – or the ones where the shooter gets fouled and misses. In other words, Total eFGS% would be the combination of Clean eFG% and Foul eFG% described in the blog entry above.

    Using this Total eFGS% would keep the number of factors at 4 but it would complicate interpreting the results . That is because the more fouls a player draws, the more his Total eFGS% will drop (because more fouls will lead to him missing more FG shots). However, a shooting foul tends to be a positive thing for the offense. So, confusingly, a drop in Total eFGS% might actually indicate a positive development regarding the offensive efficiency. Or then again, it might indicate a negative development. You couldn’t tell.

    Using Five Factors or Clean eFG% and Foul eFG% simplifies interpreting the results. The higher Clean eFG% is, the better off the offense is. And just as simply, the higher Foul eFG% is, the better off the offense is.

  2. Pingback: Blog: Remarks on Shooting and Practicing Shootin | Coach Harri Mannonen

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