# [R] Inverse Student t-value

Andre geomodelers at gmail.com
Tue Sep 30 20:45:29 CEST 2014

```Hi Duncan,

Let me explain again, I just need a manual expression for inverse student t
value.

You could go to web page
http://www.danielsoper.com/statcalc3/calc.aspx?id=10

That's inverse student t value calculator. Do you know a manual expression
use it.

Cheers!

On Wednesday, October 1, 2014, Duncan Murdoch <murdoch.duncan at gmail.com>
wrote:

> On 30/09/2014 2:26 PM, Andre wrote:
>
>> Hi Duncan,
>>
>> Actually, I am trying trace the formula for the "Critical value of Z" and
>> manual formula is =(I7-1)/SQRT(I7)*SQRT((TINV(0.
>> 05/I7,I7-2))^2/(I7-2+TINV(0.05/I7,I7-2)))
>>
>> So, I got new problem for TINV formula. I just need a manual equation for
>> TINV.
>>
>
> Sorry, can't help.  I'm not sure I understand what you want, but if it's a
> simple formula for quantiles of the t distribution, it doesn't exist.
>
> Duncan Murdoch
>
>
>> Hope solve this problem.
>>
>> Cheers!
>>
>>
>> On Wed, Oct 1, 2014 at 1:20 AM, Duncan Murdoch <murdoch.duncan at gmail.com
>> <mailto:murdoch.duncan at gmail.com>> wrote:
>>
>>     On 30/09/2014 2:11 PM, Andre wrote:
>>
>>         Hi Duncan,
>>
>>         No, that's correct. Actually, I have data set below;
>>
>>
>>     Then it seems Excel is worse than I would have expected.  I
>>     confirmed R's value in two other pieces of software,
>>     OpenOffice and some software I wrote a long time ago based on an
>>     algorithm published in 1977 in Applied Statistics. (They are
>>     probably all using the same algorithm.  I wonder what Excel is doing?)
>>
>>         N= 1223
>>         alpha= 0.05
>>
>>         Then
>>         probability= 0.05/1223=0.0000408831
>>         degree of freedom= 1223-2= 1221
>>
>>         So, TINV(0.0000408831,1221) returns 4.0891672
>>
>>
>>         Could you show me more detail a manual equation. I really
>>         appreciate it if you may give more detail.
>>
>>
>>     I already gave you the expression:  abs(qt(0.0000408831/2,
>>     df=1221)). For more detail, I suppose you could look at the help
>>     page for the qt function, using help("qt").
>>
>>     Duncan Murdoch
>>
>>
>>         Cheers!
>>
>>
>>         On Wed, Oct 1, 2014 at 1:01 AM, Duncan Murdoch
>>         <murdoch.duncan at gmail.com <mailto:murdoch.duncan at gmail.com>
>>         <mailto:murdoch.duncan at gmail.com
>>         <mailto:murdoch.duncan at gmail.com>>> wrote:
>>
>>             On 30/09/2014 1:31 PM, Andre wrote:
>>
>>
>>                 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?
>>
>>
>>
>>             That number looks pretty far off the true value. Have you
>>         got a
>>
>>             abs(qt(0.0000408831/2, df=1221)), but you'll get 4.117.
>>
>>             Duncan Murdoch
>>
>>
>>
>>
>>
>>
>

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