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MANNWHIT.DOC
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1988-07-24
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MANN-WHITNEY U-TEST -OR- TWO SAMPLE RANK TEST
AIM: This is a non-parametric test. Such tests make no assumptions about
the normality of the population distribution and do not require that the
measurements be very precise, provided only that they may be arranged
meaningfully in a rank order. It is applied here to two sample means, and
the program calculates U and U`. To test for significance, a table,
"Critical Values of U in the Two Sample Rank Test", is consulted.
EXAMPLE: In an experiment, five control (untreated) and six experimental
(drug treated) rats were studied. Blood glucose was measured in each rat.
BLOOD GLUCOSE, mg/ml FORMAT FOR DATA ENTRY FROM FILE
CONTROLS DRUG TREATED Controls <--- title for first group
2.15 2.02 5 <--- N for first group
1.92 1.71 2.15 <--- data point 1
1.78 2.04 1.92 .
2.04 1.50 1.78 .
2.22 1.83 2.04 .
1.69 2.22 .
Drug Treated <--- title for second group
6 <--- N for second group
2.02 <--- data point 1
1.71 .
2.04 .
1.50 .
1.83 .
1.69 .
Note that the raw data is rearranged in ranked form, and both the raw data
and the results are printed out. Note also that 5.5 + 24.5 = 30, and that
6 X 5 = 30. The smaller U (5.5) is compared with the critical value in the
table mentioned above. In this case, the critical value for N = 5 and N` =
6 in the table is 5, at the 5% level. Since 5.5 is not less than 5, the
drug was not effective at the 5% level.
REFERENCE: Goldstein, A. 1964 Biostatistics: An Introductory Text.
Macmillan Company, New York. Pages 55-57 and Table 15.
BASIC VERSION: Dr. Stanley Kaplan Sep 83
PASCAL VERSION: Dr. Stanley Kaplan Oct 85
UPDATES: Oct 86 (Version 2.00)
Feb 87 (Version 2.10)
Feb 88 (MS-DOS Version 2.2)