Distribution-Free Two-Sample Tests for Scale

Abstract

Abstract Several linear rank statistics have been proposed in the literature for the two-sample scale problem. We propose a new class of statistics which are distribution free when the populations are identical, but are not linear rank statistics. Our analogs of the Ansari-Bradley, Mood, and Klotz tests are of particular interest. Each has the same Pitman efficiency as its corresponding linear rank statistic, and yet our small-sample power is significantly higher. In addition, our tests are consistent for scale differences with unequal location in the case when the populations are symmetric and the sample sizes are equal.