Combined efficiency is the number of points a team would gain or lose in 100 possessions. Take a team’s offensive efficiency and subtract the defensive efficiency.
Combined Efficiency = OE - DE
Using the same example of the 2018 Championshp Game between Virginia and Texas Tech, Virginia’s offensive efficiency was 121 and its defensive efficiency was 109.
The Cavaliers combined efficiency is 12.
Combined Efficiency = 121 - 109 = 8
This gives a team 1 efficiency number instead of 2. It can be described as a glorified margin of victory.
Virginia’s combined efficiency is 12. It won the game by 8 points.
Remember the game didn’t feature 100 possessions. Combined efficiency accounts for 100 possessions. If it did, this suggests Virginia would have won by 12 points.
Offensive and defensive efficiency tell you how effective a team is based on the four factors. Combined efficiency leaves a lot unknowns as to why a team is good or bad.
If all you’re given is a combined efficiency of 12, it’s hard to know if a team is good offensively or defensively, and what factors are leading to that success.