Levene's test
is a nonparametric
test that is used to test equality
of variance when when there are two or more
samples. The hypothesis
for Levene's test is:
H_{0} the samples are drawn from
populations with equal variances
H_{1} the variance of at least
one of the populations is different
The test uses the statistic 'W' where:
Where:
N 
total number of values 
N_{i} 
number of values in row 'i' 
k 
number of levels 

median of level 'i' 

the average of all the z_{ij}
values 

the average of the z_{ij}
values in row 'i' 
The ANOVA
method relies on the assumption that the
variance is the same for all the samples.
Levene's test can be used to check this. 