Levene's test is a nonparametric test that is used to test equality of variance when there are several (more than two) 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.
