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Re: REGRESS Question [message #36721 is a reply to message #31982]

Wed, 22 October 2003 06:03

wmconnolley
Messages: 106
Registered: November 2000

Senior Member

"Christopher Lee" <cl> wrote:
> "Kevin M. Lausten" <kevinlausten@hotmail.com> wrote:

>> I am having difficulty working with the REGRESS function. I continually
>> get values <1 for my slope when doing a regression between two vectors.
>> When I do a regression mapping y to x (slope = regress(x, y, const =
>> const)) and when I do a regression mapping x to y (slope = regress(y, x,
>> const = const) I get a slope<1 for both calculations. Shouldn't the
>> y=mx+b of these two regressions be inverses of each other (leading to
>> one slope>1, and one<1?) Maybe I am misunderstanding regressions?

You've certainly misunderstood some basic maths: the inverse (as in
reciprocal) of -1 is -1, not 1. If the regression of y against x
has a negative slope, then you would expect the regression of x against y
to have too.

OTOH the relation is *not* reciprocal anyway, unless the fit is perfect.
(probably because the fit is asymmetric: y values are assumed uncertain,
x values exact).

-W.

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William M Connolley | wmc@bas.ac.uk | http://www.antarctica.ac.uk/met/wmc/
Climate Modeller, British Antarctic Survey | Disclaimer: I speak for myself
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[Message index]

		REGRESS Question By: David Fanning on Wed, 04 September 2002 14:21
		Re: REGRESS Question By: Mike Alport on Fri, 06 September 2002 00:26
		Re: REGRESS Question By: julia[1] on Thu, 05 September 2002 11:31
		Re: REGRESS Question By: William Clodius on Thu, 05 September 2002 10:31
		Re: REGRESS Question By: justspam03 on Wed, 22 October 2003 07:01
		Re: REGRESS Question By: wmconnolley on Wed, 22 October 2003 06:03
		Re: REGRESS Question By: Chris Lee on Wed, 22 October 2003 03:44
		Re: regress question By: Wout De Nolf on Mon, 01 December 2008 00:38
		Re: regress question By: mccreigh on Sun, 30 November 2008 23:42
		Re: regress question By: Kenneth P. Bowman on Sat, 29 November 2008 07:58
		Re: regress question By: Brian Larsen on Thu, 27 November 2008 07:37
		Re: regress question By: Wout De Nolf on Thu, 27 November 2008 02:47

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