Section 7.8 -- Probability Functions

PROBNORM

The PROBNORM function returns the probability that an observation from the 
standard normal distribution is less than or equal to x. 

x=probnorm(1.96);

x=0.9750021049

To compute the 2-sided pvalue, enter the following statement:

p_val = 2*(1-Probnorm(ABS(1.96)));

p_val = 0.0499957903


 
PROBT

The PROBT function returns the probability that an observation from a
Student's t distribution is less than or equal to x. The distribution has
degrees of freedom df and noncentrality parameter nc. This function
accepts a noninteger degree of freedom parameter df. If the optional
parameter, nc, is not specified or has the value 0, the value that is
returned is from the central Student's t distribution.

The significance level of a two-tailed t test is given by:

 ProbT = 2*(1-probt(abs(x),df));