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https://issues.apache.org/jira/browse/MATH-582?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13047318#comment-13047318
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Christopher Nix edited comment on MATH-582 at 6/10/11 5:47 PM:
---------------------------------------------------------------
Added a patch for org.apache.commons.math.stat.Percentile documentation in
order to better describe the correct implementation percentiles as recommended
by NIST.
was (Author: joubert):
Ammendment to org.apache.commons.math.stat.Percentile documentation to
better describe a correct implementation of NIST recommended percentiles.
> Percentile does not work as described in API
> --------------------------------------------
>
> Key: MATH-582
> URL: https://issues.apache.org/jira/browse/MATH-582
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 2.2
> Reporter: Andre Herbst
> Attachments: MATH-582.patch
>
>
> example call:
> StatUtils.percentile(new double[]{0d, 1d}, 25) returns 0.0
> The API says that there is a position being computed: p*(n+1)/100 -> we have
> p=25 and n=2
> I would expect position 0.75 as result. Next step according to the API is:
> interpolation between both values at floor(0.25) and at ceil(0.25). Those
> values are 0d and 1d ... so lower + d * (upper - lower) should give 0d +
> 0.25*(1d - 0d) = 0.25
> But the above call returns 0 as result. This does not make sense to me.
> another example where I think the result is not correct:
> StatUtils.percentile(new double[]{0d, 1d, 1d, 1d}, 25) returns 0.25
> we have pos = 25*5/100 = 1.25 ... so d = 0.25
> values at position floor(1.25) and ceil(1.25) are 1d and 1d. How comes that
> the result is not between 1d?
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