[R] Calculating p-value for 1-tailed test in a linear model

[Campomizzi, Andrew J]

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