The PROBF function returns
the probability that an observation from an
F distribution, with numerator degrees of freedom
ndf, denominator degrees of freedom
ddf, and noncentrality parameter
nc, is less than or equal to
x. The PROBF function accepts noninteger degrees
of freedom parameters
ndf and
ddf. If the optional parameter
nc is not specified or has the value 0, the value
returned is from the central
F distribution.
The significance level
for an
F test statistic is
given by
p=1-probf(x,ndf,ddf);