Perform the Ansari-Bradley test for equal scale parameters
The Ansari-Bradley test is a non-parametric test for the equality of the scale parameter of the distributions from which two samples were drawn.
- x, y : array_like
arrays of sample data
- statistic : float
The Ansari-Bradley test statistic
- pvalue : float
The p-value of the hypothesis test
The p-value given is exact when the sample sizes are both less than 55 and there are no ties, otherwise a normal approximation for the p-value is used.
 Sprent, Peter and N.C. Smeeton. Applied nonparametric statistical methods. 3rd ed. Chapman and Hall/CRC. 2001. Section 5.8.2.