The historical development of the two-sample rank-sum test is explored. While most textbooks and journal articles attribute the origin of the two-sample rank-sum test to Wilcoxon (1945) and/or Mann and Whitney (1947), the test was independently developed by at least six researchers in the late 1940s and early 1950s. In addition to Wilcoxon and Mann and Whitney, Festinger (1946), Whitfield (1947...