The F Test
is used to compare the variances of two
samples to test the hypothesis
that the samples are drawn from
populations with different variances:
H_{0} the samples are drawn from
populations with equal variances
H_{1} the samples are drawn from
populations with different variances
The F test is based on the ratio of the
variances of the two samples:

1 
2 
3 
4 
5 
Variance 
Sample A 
8.7 
9.8 
12.2 
12.9 
9.5 
3.327 
Sample B 
23.8 
21.5 
18.3 
24.3 
22.9 
5.788 
This gives an F statistic:
(Most tables give critical
values greater than 1, so divide the larger
by the smaller)
This can be compared to the critical F
value from tables, or the pvalue
can be obtained using the Excel function:
=FDIST(F_{o}, DOF_{n},
DOF_{d}) = 0.302
DOF_{n} and DOF_{d} are the Degrees
of Freedom of the numerator and denominator
(both are 4 in this example)
The F Test is based on the
F
Distribution.
