The endurance time of 24 rats in two groups in a rotating cylinder.
A data frame with 24 observations on the following 2 variables.
the endurance time
a factor with levels
The 24 rats received a fixed oral dose of a centrally acting muscle relaxant (treatment) or a saline solvent (control). They were placed on a rotating cylinder and the length of time each rat remains on the cylinder is measured, up to a maximum of 300 seconds. The rats were randomly assigned to the control and treatment group.
Note that the empirical variance in the control group is 0 and that the group medians are identical.
This dataset serves as the basis of an comparision of the results of the Wilcoxon-Mann-Whitney test computed by 11 statistical packages in Bergmann et al. (2000). The exact conditional p-value is $0.0373$ (two-sided) and $0.0186$ (one-sided). The asymptotic two-sided p-value (corrected for ties) is reported as $0.0147$.
Reinhard Bergmann, John Ludbrook & Will P.J.M. Spooren (2000), Different outcomes of the Wilcoxon-Mann-Whitney test from different statistics packages. The American Statistician, 54(1), 72–77.
data(rotarod) wilcox.exact(time ~ group, data=rotarod, alternative="g") wilcox.exact(time ~ group, data=rotarod, conf.int=TRUE) wilcox.exact(time ~ group, data=rotarod, exact=FALSE) # the permutation test perm.test(time ~ group, data=rotarod) perm.test(time ~ group, data=rotarod, exact=FALSE)
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