MATLAB: How to calculate 2-tailed P value using t value and degree of freedom

2 tailed p value

Hi all, I have gotten the t value and degree of freedom of paired data in T-Test .I need to calculate the 2-tailed P value using t value and degree of freedom.I know that the function 'tcdf' can calculate 1-tailed P value.But I still don't know how to calculate 2-tailed P value. I will be very appreciate your answers. Thank you!

Best Answer

You can simply cut to the chase and calculate it directly:

tdist2T = @(t,v) (1-betainc(v/(v+t^2),v/2,0.5));    % 2-tailed t-distribution

where ‘t’ is the t-statistic and ‘v’ the degrees-of-freedom.

Related Solutions

MATLAB: Obtaining the p value from the t stat

If you have the Statistics Toolbox, the tcdf function will do what you want.

If not, the t-probability calculation is a one-line anonymous function:

tdist2T = @(t,v) (1-betainc(v/(v+t^2),v/2,0.5));    % 2-tailed t-distribution
tdist1T = @(t,v) 1-(1-tdist2T(t,v))/2;              % 1-tailed t-distribution

where ‘t’ is the t-statistic and ‘v’ are the degrees-of-freedom. (Note that ‘tdist1T’ calls ‘tdist2T’.)

MATLAB: Function ztest not found in R2015a

You have to have the Statistics and Machine Learning Toolbox.

The core MATLAB functions erfc and erfcinv can emulate the normal probability distributions:

P = @(z) erfc(-z/sqrt(2))/2;                  % Equivalent to ‘normcdf’
CV = @(alpha) -sqrt(2) * erfcinv(2*alpha);    % Equivalent to ‘norminv’

and the t-distribution is a one-line anonymous function:

tdist2T = @(t,v) (1-betainc(v/(v+t^2),v/2,0.5));    % 2-tailed t-distribution
tdist1T = @(t,v) 1-(1-tdist2T(t,v))/2;              % 1-tailed t-distribution

where ‘t’ is the t-statistic and ‘v’ the degrees-of-freedom.

Best Answer

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MATLAB: Obtaining the p value from the t stat

MATLAB: Function ztest not found in R2015a

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