[R] T-test & for loop

[Greg Snow]

Golf entry:

mean( replicate( 10000, t.test(rnorm(10, 0.1, 1), alternative='greater', mu=0, conf.level=0.95)$p.value < 0.05))

Or
 
mean( replicate( 10000, t.test(rnorm(10, .1), a='g')$p.value < .05))

or even

mean( replicate( 10000, t.test(rnorm(10, .1), a='g')$p. < .05))

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Joris Meys
> Sent: Thursday, May 06, 2010 9:57 AM
> To: Dimitri Liakhovitski
> Cc: r-help at r-project.org; level
> Subject: Re: [R] T-test & for loop
> 
> Hehe,
> 
> those homeworks. If you can explain this code to the professor, you
> surely
> passed.
> 
> n <-10000
> obs.rej.rate <- sum(sapply(1:n,function(x){t.test(rnorm(10, 0.1,
> 1),alternative="greater",mu=0,conf.level=0.95)$p.value <0.05}))/n
> obs.rej.rate
> 
> This could actually be another round of R-golf. Anybody up to it?
> 
> 
> 
> On Thu, May 6, 2010 at 3:03 AM, Dimitri Liakhovitski
> <ld7631 at gmail.com>wrote:
> 
> > Sounds like homework (you are not supposed to post homework-related
> > questions here - read the guidelines). But anyway:
> >
> > nr.of.rejections=0
> > for(i in 1:10000){
> >     x=rnorm(10, 0.1, 1)
> >     result<-
> t.test(x,alternative="greater",mu=0,conf.level=0.95)$p.value
> >    if(result<0.05) nr.of.rejections = nr.of.rejections+1
> > }
> > print(paste("Observed number of rejections of Ho:", nr.of.rejections,
> sep="
> > "))
> > observed.rejection.rate = nr.of.rejections/10000
> > print(paste("Actual rejection rate of Ho:", observed.rejection.rate,
> sep="
> > "))
> >
> > However, it's not Type 1 error rate. It's the observed rejection
> rate. Type
> > 1 error is probability of rejecting Ho when it is actually TRUE. And
> in
> > your
> > case (x = rnorm(10,0.1,1) your null hypothesis (that mean = 0) is NOT
> true
> > because,as you know, in the population the mean is 0.1.
> >
> > Dimitri
> >
> >
> > On Wed, May 5, 2010 at 2:31 PM, level <lev_lambert at hotmail.co.uk>
> wrote:
> >
> > >
> > > I have been set a question which i understand statistically but my
> > > inability
> > > with R is preventing me from finishing it..
> > >
> > > My question is that we to calculate the frequency of Type 1 errors
> > >
> > > starting with  x = rnorm(10, 0.1, 1)
> > >
> > > then doing a t-test seeing whether you reject the null hypothesis
> (Ho
> >  mu
> > > =
> > > 0) alternative is mu > 0
> > >
> > > Then i am supposed to use a for loop to do this procedure 10 000
> times
> > > keeping track whether the null has been rejected or not.  If anyone
> can
> > > help
> > > with me it would be great help
> > >
> > > cheers
> > >
> > > --
> > > View this message in context:
> > > http://r.789695.n4.nabble.com/T-test-for-loop-
> tp2131458p2131458.html
> > > Sent from the R help mailing list archive at Nabble.com.
> > >
> > > ______________________________________________
> > > R-help at r-project.org mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide
> > > http://www.R-project.org/posting-guide.html
> > > and provide commented, minimal, self-contained, reproducible code.
> > >
> >
> >
> >
> > --
> > Dimitri Liakhovitski
> > Ninah.com
> > Dimitri.Liakhovitski at ninah.com
> >
> >        [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> 
> 
> 
> --
> Joris Meys
> Statistical Consultant
> 
> Ghent University
> Faculty of Bioscience Engineering
> Department of Applied mathematics, biometrics and process control
> 
> Coupure Links 653
> B-9000 Gent
> 
> tel : +32 9 264 59 87
> Joris.Meys at Ugent.be
> -------------------------------
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> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
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