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Re: Box-Whisker plots in IDL [message #55391 is a reply to message #55390]

Mon, 20 August 2007 16:04

jschwab@gmail.com
Messages: 30
Registered: December 2006

Member

Pardon me if I'm mistaken, but I think these "quartiles with
histogram" examples, including the one that's in JD's histogram
tutorial are fundamentally incorrect.

You are assuming "Equal bin widths" ==> "Equal #'s in each bin" !

When HISTOGRAM splits a data list into N bins, it does so such that
the *width* of the bins are equal. In no way does it somehow create a
situation in which the *number of points* in each bin is equal (which
is what would be required to find quartiles in such a manner).

The given examples have only "worked" because you're either dealing
with uniform distributions (in which case equal bin widths do imply
equal numbers in each bin) or because the example data happens to be
roughly uniform.

If you want to convince yourself, try one of those codes with
data = randomu(seed, 1000) * 100.
and then with
data2 = data * data
The quartiles in the 2nd case should simply be the squares of the
quartiles from the first.

Cheers,
Josiah
--
Josiah Schwab
MIT, Course VIII

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[Message index]

		Re: Box-Whisker plots in IDL By: David Fanning on Mon, 20 August 2007 21:01
		Re: Box-Whisker plots in IDL By: Marshall Perrin on Mon, 20 August 2007 17:37
		Re: Box-Whisker plots in IDL By: jschwab@gmail.com on Mon, 20 August 2007 17:06
		Re: Box-Whisker plots in IDL By: David Fanning on Mon, 20 August 2007 16:47
		Re: Box-Whisker plots in IDL By: jschwab@gmail.com on Mon, 20 August 2007 16:04
		Re: Box-Whisker plots in IDL By: teich on Mon, 20 August 2007 14:03
		Re: Box-Whisker plots in IDL By: David Fanning on Mon, 20 August 2007 13:56
		Re: Box-Whisker plots in IDL By: teich on Mon, 20 August 2007 13:22
		Re: Box-Whisker plots in IDL By: David Fanning on Mon, 20 August 2007 12:40
		Re: Box-Whisker plots in IDL By: teich on Mon, 20 August 2007 12:18
		Re: Box-Whisker plots in IDL By: Brian Larsen on Mon, 20 August 2007 12:01
		Re: Box-Whisker plots in IDL By: teich on Mon, 20 August 2007 10:27
		Re: Box-Whisker plots in IDL By: David Fanning on Mon, 20 August 2007 10:10
		Re: Box-Whisker plots in IDL By: mankoff on Mon, 20 August 2007 10:04
		Re: Box-Whisker plots in IDL By: JD Smith on Sun, 26 August 2007 18:50
		Re: Box-Whisker plots in IDL By: jschwab@gmail.com on Mon, 20 August 2007 21:46

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