A Wilcoxon rank sum test for comparing two populations involves two independent samples of sizes 15 and 20. If the value of un-standardized test statistic is T = 225, then the value of the standardized test statistic is z = -1.50.

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Quizplus · Accepted Answer

This is true. The standardized test statistic for a Wilcoxon rank sum test can be calculated using the formula z = (T - μT) / σT, where T is the un-standardized test statistic, μT is its expected value (which is equal to n1 * (n1 + n2 + 1) / 2), and σT is the standard deviation of T (which is equal to sqrt(n1 * n2 * (n1 + n2 + 1) / 12)). Plugging in the given values, we get:

z = (225 - 150) / sqrt(15 * 20 * (15 + 20 + 1) / 12) = -1.50

Therefore, the given value of z is correct.

A Wilcoxon Rank Sum Test for Comparing Two Populations Involves