Date: Fri, 11 Mar 2011 08:38:28 -0800
Reply-To: apb218 <email@example.com>
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From: apb218 <firstname.lastname@example.org>
Subject: Percentiles and Ties
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I have a client who wants me to report on the amount spent by the Top X
Percentile of Customers in each of the last three years.
I tried using the Percentiles within the Rank command, but I learned that
there are a lot of ties in my data, and none of the options for handling
ties (mean, high, low, sequential) seems to handle them in what I would
consider the right way.
The problem is that each seems to produces a "lumpy" distribution; none of
them seems to give me exactly 10% of customers in each decile because (I
think) they will all assign people with the same revenue the same rank and
therefore the same percentile.
My preference would be a method that assigns some of the ties to the higher
percentile and some to the lower percentile at random; the point is to
finish in a place where exactly 10% of the cases are in each decile.
Is there another way?
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