[R] t-distribution

Wed Aug 1 21:42:14 CEST 2007

Indeed, this is what I wanted, I figured it from the function you and
Mark pointed me. Thank you both. 

I am trying to plot it to illustrate the point and I tried this

plot(function(x) dt(x, df = 9), -5, 5, ylim = c(0, 0.5), main="t -
Density", yaxs="i")

Is there an easy way to shade the area under the curve? 

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of
Bill.Venables at csiro.au
Sent: Wednesday, August 01, 2007 3:18 PM
To: bolker at ufl.edu; r-help at stat.math.ethz.ch
Subject: Re: [R] t-distribution

Well, is "t = 1.11" all that accurate in the first place?  :-)

In fact, reading beween the lines of the original enquiry, what the
person probably wanted was something like

ta <- pt(-1.11, 9) + pt(1.11, 9, lower.tail = FALSE)

which is the two-sided t-test tail area.

The teller of the parable will usually leave some things unexplained...

Bill. 

Bill Venables
CSIRO Laboratories
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http://www.cmis.csiro.au/bill.venables/ 

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Ben Bolker
Sent: Thursday, 2 August 2007 4:57 AM
To: r-help at stat.math.ethz.ch
Subject: Re: [R] t-distribution

 <Bill.Venables <at> csiro.au> writes:

> 
> for the upper tail:
> 
> > 1-pt(1.11, 9)
> [1] 0.1478873
> 
   wouldn't 
     pt(1.11, 9, lower.tail=FALSE)
  be more accurate?

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