# [ncl-talk] Help in using betainc function

Dennis Shea shea at ucar.edu
Fri Apr 26 07:16:22 MDT 2019

```*http://www.ncl.ucar.edu/Document/Functions/Built-in/betainc.shtml*
<http://www.ncl.ucar.edu/Document/Functions/Built-in/betainc.shtml>

See Example 2

df   = 20
tval = 2.08
prob = *betainc*( df/(df+tval^2), df/2.0, 0.5)

So: x = df/(df+tval^2)
a = df/2.0
b = 0.5

As noted in the "Description" section.

This returns the same results as in the "Numerical Recipes" text.

Good luck

On Thu, Apr 25, 2019 at 11:48 PM Dr. Alvarinho J. Luis <alvluis1 at gmail.com>
wrote:

> Dear all,
>
>   I am struggling on how to use* betainc *function to compute
> significance (or  probability) at p<0.05 (95% probability) using three
> dimensional variable:  I have sea ice concentration fields for 23 years .
> I would like to compute the significance of the sea ice concentration trend
> using betainc...
>
> for df=23-2=21
> student t statistic at 95% with two tailed test= 2.069
>
> prob = (1.-*betainc*(x,a,b))*100.
>
> what is x, a and b ?
>
> how to obtain 95% probability ?
> I am struggling to implement this function for three dimensional (x,y,t)
> fields
>
>
> Thanks & regards,
> Luis
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