R help - Aug 2011 - Calculating p-value for 1-tailed test in a linear model

Hello,

I'm having trouble figuring out how to calculate a p-value for a 1-tailed
test of beta_1 in a linear model fit using command lm.  My model has only 1
continuous, predictor variable.  I want to test the null hypothesis beta_1
is >= 0.  I can calculate the p-value for a 2-tailed test using the code
"2*pt(-abs(t-value), df=degrees.freedom)", where t-value and
degrees.freedom
are values provided in the summary of the lm.  The resulting p-value is the
same as provided by the summary of the lm for beta_1.  I'm unsure how to
change my calculation of the p-value for a 1-tailed test.

Thanks for your assistance,

Andy


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On 20/08/11 10:20, Andrew Campomizzi wrote:
> Hello,
>
> I'm having trouble figuring out how to calculate a p-value for a
1-tailed
> test of beta_1 in a linear model fit using command lm.  My model has only 1
> continuous, predictor variable.  I want to test the null hypothesis beta_1
> is>= 0.  I can calculate the p-value for a 2-tailed test using the code
> "2*pt(-abs(t-value), df=degrees.freedom)", where t-value and
degrees.freedom
> are values provided in the summary of the lm.  The resulting p-value is the
> same as provided by the summary of the lm for beta_1.  I'm unsure how
to
> change my calculation of the p-value for a 1-tailed test.
>
> Thanks for your assistance,
>
> Andy
The r-help mailing list is *not* for giving assistance with homework.

     cheers,

         Rolf Turner

My question isn't related to homework.  It is a small part of an actual
problem I'm trying to solve.  I've been unable to find a solution in R
help files and discussions, in statistics books, or from colleagues.  The
solution may not be overly complicated, but any assistance is appreciated.
Thanks,
Andy

----- Original Message -----
From: "Rolf Turner" <rolf.turner at xtra.co.nz>
To: "Andrew Campomizzi" <acampomizzi at tamu.edu>
Cc: r-help at r-project.org
Sent: Friday, August 19, 2011 9:18:07 PM GMT -06:00 US/Canada Central
Subject: Re: [R] Calculating p-value for 1-tailed test in a linear model

The r-help mailing list is *not* for giving assistance with homework.

     cheers,

         Rolf Turner


On 20/08/11 10:20, Andrew Campomizzi wrote:
> Hello,
>
> I'm having trouble figuring out how to calculate a p-value for a
1-tailed
> test of beta_1 in a linear model fit using command lm.  My model has only 1
> continuous, predictor variable.  I want to test the null hypothesis beta_1
> is>= 0.  I can calculate the p-value for a 2-tailed test using the code
> "2*pt(-abs(t-value), df=degrees.freedom)", where t-value and
degrees.freedom
> are values provided in the summary of the lm.  The resulting p-value is the
> same as provided by the summary of the lm for beta_1.  I'm unsure how
to
> change my calculation of the p-value for a 1-tailed test.
>
> Thanks for your assistance,
>
> Andy

On Aug 19, 2011, at 6:20 PM, Andrew Campomizzi wrote:
> Hello,
>
> I'm having trouble figuring out how to calculate a p-value for a 1- 
> tailed
> test of beta_1 in a linear model fit using command lm.  My model has  
> only 1
> continuous, predictor variable.  I want to test the null hypothesis  
> beta_1
> is >= 0.  I can calculate the p-value for a 2-tailed test using the  
> code
> "2*pt(-abs(t-value), df=degrees.freedom)", where t-value and  
> degrees.freedom
> are values provided in the summary of the lm.  The resulting p-value  
> is the
> same as provided by the summary of the lm for beta_1.  I'm unsure  
> how to
> change my calculation of the p-value for a 1-tailed test.
You need to clearly state your hypothesis. Then using the output from  
the regression function should be straightforward.

(Yes. this is a intentionally vague answer designed to elicit further  
information about your understanding of the statistical issues and how  
they relate to your domain knowledge. Many time peole already have the  
data and because they didn't get the answer they wanted, they search  
for other ways to "game the system" by ad-hoc changes in the  
statistical "rules of the road".)

--

David Winsemius, MD
West Hartford, CT