The PROBT function returns
the probability that an observation from a Student's
t distribution, with degrees of freedom
df and noncentrality parameter
nc, is less than or equal to
x. 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
p=(1-probt(abs(x),df))*2;