There are three group ratings, the "central mean", the
"simple average" (also known as the "arithmetic mean",)
and the WIN50%.
The "central mean" gives the most weight to the middle team(s)
in the group and progressively less weight to teams as you go
away from the middle in either direction, up or down.
This tends to smooth out the effect of anomalous teams that are rated
much higher and lower than the middle team(s) in the group. The
"simple average" ("arithmetic mean") weights each team equally
no matter where they are relative to the middle.
Here are a few examples of how the "central mean" is computed.
4-team group ___ the weights are 1-2-2-1
5-team group ___ the weights are 1-2-3-2-1
6-team group ___ the weights are 1-2-3-3-2-1
7-team group ___ the weights are 1-2-3-4-3-2-1
8-team group ___ the weights are 1-2-3-4-4-3-2-1
9-team group ___ the weights are 1-2-3-4-5-4-3-2-1
10-team group ___ the weights are 1-2-3-4-5-5-4-3-2-1
11-team group ___ the weights are 1-2-3-4-5-6-5-4-3-2-1
12-team group ___ the weights are 1-2-3-4-5-6-6-5-4-3-2-1
13-team group ___ the weights are 1-2-3-4-5-6-7-6-5-4-3-2-1
This is an expanded version of the "tri-mean".
The WIN50% is the rating required to win 50% of the games if playing an
infinite number of round-robins in the given group at a neutral location.
CONFERENCE CENTRAL MEAN SIMPLE AVERAGE TEAMS WIN50%
1 SEC-WEST (A) = 86.73 86.63 ( 1) 7 86.59 ( 1)
2 PAC-12(NORTH) (A) = 78.34 78.20 ( 4) 6 78.34 ( 3)
3 PAC-12(SOUTH) (A) = 78.16 77.88 ( 5) 6 77.93 ( 5)
4 ACC-ATLANTIC (A) = 77.88 78.24 ( 3) 7 78.03 ( 4)
5 BIG 12 (A) = 77.76 76.57 ( 7) 10 77.29 ( 6)
6 ACC-COASTAL (A) = 77.11 76.70 ( 6) 7 76.85 ( 7)
7 BIG TEN-EAST (A) = 76.82 78.43 ( 2) 7 78.38 ( 2)
8 BIG TEN-WEST (A) = 73.77 73.33 ( 9) 7 73.60 ( 9)
9 SEC-EAST (A) = 73.32 74.12 ( 8) 7 73.86 ( 8)
Actually its SEC West then Big Ten East then ACC Atlantic/Pac12 north