R help - Nov 2007 - how to find critical values of t in R

Hi,

I am trying to find a function in R that would calculate the critical value
of t for a given probability and df. For example, if p=5% and df=20, then
does R have a function to calculate the t value? I tried:
> dt(0.05,df=20)
[1] 0.3934718

That doesn't look right to me. Could someone tell me what I was missing?

Thanks,

-- 
Tom

	[[alternative HTML version deleted]]

tom soyer wrote:
> Hi,
>
> I am trying to find a function in R that would calculate the critical value
> of t for a given probability and df. For example, if p=5% and df=20, then
> does R have a function to calculate the t value? I tried:
>
>   
>> dt(0.05,df=20)
>>     
> [1] 0.3934718
>
> That doesn't look right to me. Could someone tell me what I was
missing?
>
> Thanks,
>
>   
qt()

Notice that it gives only one tail (to the left by default), so you need
p/2 for two-sided tests.

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