Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support

Different Outcomes of the Wilcoxon-Mann-Whitney Test from Different Statistics Packages

Reinhard Bergmann, John Ludbrook and Will P. J. M. Spooren
The American Statistician
Vol. 54, No. 1 (Feb., 2000), pp. 72-77
DOI: 10.2307/2685616
Stable URL: http://www.jstor.org/stable/2685616
Page Count: 6
  • Download ($14.00)
  • Cite this Item
If you need an accessible version of this item please contact JSTOR User Support
Different Outcomes of the Wilcoxon-Mann-Whitney Test from Different Statistics Packages
Preview not available

Abstract

The Wilcoxon-Mann-Whitney test enjoys great popularity among scientists comparing two groups of observations, especially when measurements made on a continuous scale are non-normally distributed. Triggered by different results for the procedure from two statistics programs, we compared the outcomes from 11 PC-based statistics packages. The findings were that the delivered p values ranged from significant to nonsignificant at the 5% level, depending on whether a large-sample approximation or an exact permutation form of the test was used and, in the former case, whether or not a correction for continuity was used and whether or not a correction for ties was made. Some packages also produced pseudo-exact p values, based on the null distribution under the assumption of no ties. A further crucial point is that the variant of the algorithm used for computation by the packages is rarely indicated in the output or documented in the Help facility and the manuals. We conclude that the only accurate form of the Wilcoxon-Mann-Whitney procedure is one in which the exact permutation null distribution is compiled for the actual data.

Page Thumbnails

  • Thumbnail: Page 
72
    72
  • Thumbnail: Page 
73
    73
  • Thumbnail: Page 
74
    74
  • Thumbnail: Page 
75
    75
  • Thumbnail: Page 
76
    76
  • Thumbnail: Page 
77
    77