Introducing: Expected Margin (EM)

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I have updated my rankings to included an expected margin number alongside the original rating, which is the result of a cumulative distribution function of the ratings vector. The old ratings are displayed under the CDF Rating heading and the expected margins are displayed under the EM header.

The expected margin value is the expected margin of loss/victory for a given team against an average team over 100 possessions. “Average team,” here, is a hypothetical team with a rating that is the average of all Division I team ratings (Note: This is not the same as a median team. My ratings are skewed in the direction of higher ranking teams, which means that the average team is a lot better than the median team.) And 100 possessions were chosen simply because it is a nice number, and the numbers are easier to read than a 1-possession EM.

Expected margin is usually calculated as the difference between offensive efficiency and defensive efficiency. However, my expected margin numbers are based on a model of my ratings.

Expected margin has the benefit of being a linear value. For example, the difference between a +14 EM team and a +10 EM team is the same as the difference between a 0 EM team and a -4 EM team. This makes EM a more useful rating tool than the CDF ratings.

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