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@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@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@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@ninah.com
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@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.
>



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Department of Applied mathematics, biometrics and process control

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