coin (version 1.0-24)

rotarod: Rotating Rats Data

Description

The endurance time of 24 rats in two groups in a rotating cylinder.

Usage

data("rotarod")

source

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.

Details

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.

Examples

### Wilcoxon-Mann-Whitney Rank Sum Test

  ### one-sided exact (0.0186)
  wilcox_test(time ~ group, data = rotarod, 
      alternative = "greater", distribution = "exact")
  ### two-sided exact (0.0373)
  wilcox_test(time ~ group, data = rotarod, distribution = "exact")
  ### two-sided asymptotical (0.0147)
  wilcox_test(time ~ group, data = rotarod)