[SciPy-User] how does scipy.stats.t.isf work?

josef.pktd@gmai... josef.pktd@gmai...
Wed Jun 16 11:40:14 CDT 2010


On Wed, Jun 16, 2010 at 12:13 PM, neurino <neurino@gmail.com> wrote:
> Honestly the full question is
> "how does scipy.stats.t.isf work compared to common spreadsheets function
> T.INV?"
> I have to translate an excel calculation using TINV
> In all excel, ooo or abiword I get:
>
> TINV: inverse of the survival function of the Student t-distribution
> Arguments:
> p: probability
> dof: number of degrees of freedom
> The survival function is 1 minus the cumulative distribution function.
> Note: If p < 0 or p > 1 or dof < 1 this function returns a #NUM! error.
> Microsoft Excel: This function is Excel compatible.
> Examples:
> tinv(0,4;32) evaluates to 0,852998453651888.
>
> while with scipy I get:
>>>> from scipy.stats import t
>>>> t.isf(.4, 32)
> 0.25546356665122449
> Any advice welcome, please consider I'm an informatic but not a
> mathematician.
> Thanks for your support

I guess Excel uses a two-sided tail probability

>>> stats.t.isf(.4/2., 32)
0.85299845247181938

Josef


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