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Re: compute quartiles of a distribution [message #77917 is a reply to message #77916]

Tue, 18 October 2011 09:12

Thibault Garel
Messages: 55
Registered: October 2009

Member

Thanks to both of you for your answers.

The procedures in summary.pro and cgBoxPlot.pro compute "real"
quartiles. Actually, I should not have used this word in my case i
guess.

What I want is the interval [M-Q;M+Q] which encompass 75% of the
values of the sample around the mean (not the median) value M, where Q
is unique (i.e the same at lower and higher values around M). I do not
want the 37.5% above M and the 37.5% below. It makes a little
difference with what is calculated with your routines.
The idea would be to span the sample starting from the mean, and
counting the points at lower and higher values around the mean in an
iterative manner, until I have counted 75% of sample. This would give
the value of Q at which the 75% is reached. I have a crude idea to do
that with for loops but it will take forever...

If you see what I mean, and if you have a piece of code, this could
help a lot!

Thanks again.

> bing999 writes:
>> I have sample of data (which distribution is unknown) of mean M. I
>> would like to calculate the quartiles with IDL, i.e what is the value
>> of Q for which 25% (or 75%) of the sample is comprised between [M-Q;M
>> +Q] ?
>> Do you know a routine which does that?
>
> cgBoxPlot.
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.idlcoyote.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: compute quartiles of a distribution By: Jeremy Bailin on Tue, 18 October 2011 21:32
		Re: compute quartiles of a distribution By: Jeremy Bailin on Tue, 18 October 2011 12:48
		Re: compute quartiles of a distribution By: Brian Wolven on Tue, 18 October 2011 10:38
		Re: compute quartiles of a distribution By: Thibault Garel on Tue, 18 October 2011 09:36
		Re: compute quartiles of a distribution By: David Fanning on Tue, 18 October 2011 09:25
		Re: compute quartiles of a distribution By: Thibault Garel on Tue, 18 October 2011 09:12
		Re: compute quartiles of a distribution By: Thibault Garel on Tue, 18 October 2011 09:13
		Re: compute quartiles of a distribution By: David Fanning on Mon, 17 October 2011 18:26
		Re: compute quartiles of a distribution By: Vincent Sarago on Mon, 17 October 2011 06:05

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