# [R] Inverse Student t-value

Nordlund, Dan (DSHS/RDA) NordlDJ at dshs.wa.gov
Tue Sep 30 21:00:24 CEST 2014

```> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of JLucke at ria.buffalo.edu
> Sent: Tuesday, September 30, 2014 11:49 AM
> To: Andre
> Cc: r-help at r-project.org
> Subject: Re: [R] Inverse Student t-value
>
> My Excel (2013) returns exactly what R does.   I used both T.INV and
> T.INV.T2    There is no TINV.  Has Excel been updated?
>
>

I have Excel 2007, and it does have the function TINV().  And, it also returns the same value as R-3.1.1. So, there appears to be a problem with whatever unstated system and version of Excel that the OP is using.

Dan

Daniel J. Nordlund
Research and Data Analysis Division
Washington State Department of Social and Health Services

>
>
>
> Duncan Murdoch <murdoch.duncan at gmail.com>
> Sent by: r-help-bounces at r-project.org
> 09/30/2014 02:36 PM
>
> To
> Andre <geomodelers at gmail.com>,
> cc
> r-help at r-project.org
> Subject
> Re: [R] Inverse Student t-value
>
>
>
>
>
>
> 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
> >             typo in your example?
> >
> >             abs(qt(0.0000408831/2, df=1221)), but you'll get 4.117.
> >
> >             Duncan Murdoch
> >
> >
> >
> >
> >
>
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