[R] simple test on slope of lm()

Yves Brostaux brostaux.y at fsagx.ac.be
Mon Nov 25 09:32:06 CET 2002


To test the slope of your linear model against an arbitrary value, you can 
use lm() directly with a little trick. Let b1 be the value of the slope you 
want to test your model against, then use lm(y-b1*x~x). The significance 
test of the slope for this lm model gives the answer you need.

 > x <- rnorm(10)
 > y <- 2*x + rnorm(10)
 > lm(y~x)
 > lm(y-2*x~x)

Hope this helped,

Yves Brostaux.

At 04:01 23/11/02, you wrote:
>Date: Fri, 22 Nov 2002 22:08:43 +0100
>From: Fred JEAN <frederic.jean at univ-brest.fr>
>Subject: [R] simple test on slope of lm()
>I want to compare the slope (let's say 'b') of a linear model obtained
>with lm() to a theoretical value (let's say 'th').
>To do so, I think I should compute a 't value' using
>something like :
>(b - 'th')/standard.deviation(b)
>and then look at the p-value of this computed t.
>I don't understand how to do this in a simple way, just using lm()
>outputs for example.
>I'm sorry of such a naive/newbie question, and thank you so much for
>taking time to answer.

Ir. Yves Brostaux - Statistics and Computer Science Dpt.
Gembloux Agricultural University
8, avenue de la Faculté B-5030 Gembloux (Belgium)
Tél : +32 (0)81 62 24 69
E-mail : brostaux.y at fsagx.ac.be
Web : http://www.fsagx.ac.be/si/

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