A Wilcoxon rank sum test for comparing two populations involves two independent samples of sizes 15 and 20. The unstandardised test statistic (that is the rank sum) is T = 210. The value of the standardised test statistic z is:
A) 14.0.
B) 10.5.
C) 6.0.
D) -2.0.

Question

Quizplus · Accepted Answer

The standardised test statistic z is calculated using the formula: z = (T - mean of T) / standard deviation of T. For the Wilcoxon rank sum test, the mean of T is n1(n1+n2+1)/2 and the standard deviation is sqrt(n1*n2(n1+n2+1)/12). Substituting n1=15, n2=20, and T=210 into these formulas gives z = -2.0.

A Wilcoxon Rank Sum Test for Comparing Two Populations Involves