[R] How to compute p-Values

[gregor rolshausen]

Andreas Klein wrote:
> Hello.
>
>
> How can I compute the Bootstrap p-Value for a one- and two sided test, when I have a bootstrap sample of a statistic of 1000 for example?
>
> My hypothesis are for example:
>
> 1. Two-Sided: H0: mean=0 vs. H1: mean!=0
> 2. One Sided: H0: mean>=0 vs. H1: mean<0
>
>   
hi,
do you want to test your original t.test against t.tests of bootstrapped 
samples from you data?

if so, you can just write a function creating a vector with the 
statistics (t) of the single t.tests (in your case 1000 t.tests each 
with a bootstrapped sample of your original data -> 1000 simulated 
t-values).
you extract them by:

 > tvalue=t.test(a~factor)$statistic

then just calculate the proportion of t-values from you bootstrapped 
tests that are bigger than your original t-value.

 >p=sum(simualted_tvalue>original_tvalue)/1000


(or did I get the question wrong?)

cheers,
gregor