R help - Sep 2014 - Inverse Student t-value

Dear Sir/Madam,

I am trying to use calculation for two-tailed inverse of the student`s
t-distribution function presented by Excel functions like
=TINV(probability, deg_freedom).

For instance: The Excel function =TINV(0.0000408831,1221) =  returns
 4.0891672.

Would you like to show me a manual calculation for this?

Appreciate your helps in advance.


Cheers!  Andre

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On 30/09/2014 1:31 PM, Andre wrote:
> Dear Sir/Madam,
>
> I am trying to use calculation for two-tailed inverse of the student`s
> t-distribution function presented by Excel functions like
> =TINV(probability, deg_freedom).
>
> For instance: The Excel function =TINV(0.0000408831,1221) =  returns
>   4.0891672.
>
> Would you like to show me a manual calculation for this?
>
> Appreciate your helps in advance.
That number looks pretty far off the true value.  Have you got a typo in 
your example?

You can compute the answer to your question as abs(qt(0.0000408831/2, 
df=1221)), but you'll get 4.117.

Duncan Murdoch