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Garrison Keillor would be spinning etc.

Under the subject line, “Misleading Graphs of the Week,” Bill Jefferys sends along this:


I agreed with Bill’s colleague Helen Read who wondered why should the 90th percentile be some magic number? Just change it to 85% or 95% or whatever and all the graphs will look different. Also kinda horrible that they’re presenting percentages to 2 decimal places, but that’s not a graphics issue, it’s just plain old innumeracy.


  1. Martha (Smith) says:

    “why should the 90th percentile be some magic number”

    Some people just seem to have a psychological need for a “bright line” cutoff, I guess.

  2. Carlos Ungil says:

    Maybe the have set for themselves the target of being in the top 10%. A completely arbitrary threshold,, but I don’t think plotting the full empirical distribution of scores (even if they knew it) would be better.

  3. Todd T says:

    Typically, Blue Cross/Blue Shield of Vermont wouldn’t have access to the entire data set comparing all of the plans. They typically have their own data and a few percentile scores such as 90th, 75, 50, 25.

    That said, there is a lot that HEDIS and similar quality organizations could do to improve the metrics collected and shared for health plans.

  4. Jon says:

    I really don’t understand what they are trying to show here: That they are slightly worse than the 90th percentile? I would think they would have wanted to pick some percentile over 50 that they could beat.

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