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Morrison on Metrics: Trimmed Means and Weighted Averages

Trimmed means and weighted averages are less familiar ways to describe metrics than averages, medians, and quartiles. The middle figure of a sorted list of metrics (the median), the total of all the figures divided by the number of them (the average), and the midpoint between the high or low and the median (the quartiles) are standard fare. That said, the other two numbers are useful ways to describe a collection of metrics.

A trimmed mean calculation shaves off some number of extreme values. A common choice is to omit the 2 1/2 percent of the values at the low end and the 2 1/2 percent at the high end of a sorted list. Thus, if you have the ratio of inside spending to external spend for 300 law departments sorted high to low, you would drop the seven smallest ratios and the seven largest ratios. Then calculate the average (aka the mean) as normal.

Rees Morrison

Rees Morrison, Esq. is the founder of General Counsel Metrics, LLC. Based in Princeton, NJ, Rees has for the past 25 years consulted solely to...

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