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:
- Clean effective field goal percentage
- Foul effective field goal percentage
- Turnovers per possession
- Offensive rebounding percentage
- 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.