From: Corey Moffet <cmoffet_at_nwrc.ars.usda.gov>

Date: Wed 21 Jul 2004 - 04:26:10 EST

Date: Wed 21 Jul 2004 - 04:26:10 EST

At 06:44 PM 7/20/2004 +0100, Adaikalavan Ramasamy wrote:

>I would try to construct the confidence intervals and compare them to

*>the value that you want
**>> x <- rnorm(20)
**>> y <- 2*x + rnorm(20)
**>> summary( m1 <- lm(y~x) )
**>
**><snip>
**>Coefficients:
**> Estimate Std. Error t value Pr(>|t|)
**>(Intercept) 0.1418 0.1294 1.095 0.288
**>x 2.2058 0.1289 17.108 1.4e-12 ***
**><snip>
**>
**>That says that the slope estimate is 2.2058 with standard error of
**>0.1289. So the approximate 99% CI is 2.2058 +/- 3*0.1289 = (1.819,
**>2.593) which is clearly greater than 1.
*

Another method which gives the p value etc. was shared with this list by Prof. Ripley several years ago:

set.seed(1)

x <- rnorm(20)

x.hypoth <- 1 # i.e., Null hypothesis is that x != 1
y <- 2*x + rnorm(20)

summary( m1 <- lm(y - x.hypoth*x~x) )

Produces:

Call:

lm(formula = y - x.hypoth * x ~ x)

Residuals:

Min 1Q Median 3Q Max -1.69133 -0.43739 -0.07132 0.68033 1.63937

--- Signif. codes: 0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 Residual standard error: 0.8738 on 18 degrees of freedom Multiple R-Squared: 0.42, Adjusted R-squared: 0.3878 F-statistic: 13.03 on 1 and 18 DF, p-value: 0.002001Received on Wed Jul 21 04:37:28 2004

>

>> summary(m1)[[4]][2,1] + 3* summary(m1)[[4]][2,2]

>[1] 2.592629>> summary(m1)[[4]][2,1] - 3* summary(m1)[[4]][2,2]>[1] 1.819026>>For your next question, you simply compare the CI of one slope to>another and see if they overlap.>>There is probably a way to construct proper significance testing to get>p-values and such. You can try reading MASS4 or hopefully someone in the>list might provide with a neater answer.>>>On Tue, 2004-07-20 at 17:02, Avril Coghlan wrote:>> Hello,>>>> I'm a newcomer to R so please>> forgive me if this is a silly question.>>>> It's that I have a linear regression:>> fm <- lm (x ~ y)>> and I want to test whether the>> slope of the regression is significantly>> less than 1. How can I do this in R?>>>> I'm also interested in comparing the>> slopes of two regressions:>> fm1 <- lm (x ~ y)>> fm2 <- lm (a ~ b)>> and asking if the slope of fm1 is>> less than the slope of fm2. Is this>> easy to do in R?>>>>>> I will be very grateful for any help.>>>> regards,>> Avril Coghlan>> (University College Dublin, Ireland)>>>> ______________________________________________>> R-help@stat.math.ethz.ch mailing list>> https://www.stat.math.ethz.ch/mailman/listinfo/r-help>> PLEASE do read the posting guide!

http://www.R-project.org/posting-guide.html

>>>

>______________________________________________

>R-help@stat.math.ethz.ch mailing list>https://www.stat.math.ethz.ch/mailman/listinfo/r-help>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html>

With best wishes and kind regards I am Sincerely, Corey A. Moffet Rangeland Scientist ################################################################## #### USDA-ARS # Northwest Watershed Research Center # 800 Park Blvd, Plaza IV, Suite 105 ########### #### Boise, ID 83712-7716 # # # # Voice: (208) 422-0718 # # #### #### FAX: (208) 334-1502 # # # # #### ########### ################################################################## ______________________________________________ R-help@stat.math.ethz.ch mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html

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