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Thread: how to arrange data in Mann - Whitney U test

  1. #1
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    how to arrange data in Mann - Whitney U test




    Hi,
    I have a data for pH of groundwater samples from four sites in first season and three sites in second season. I wanted to apply the Mann whitney U test to compare the groups.

    In first season raw data of pH for four sites analysed in triplicate and mean value for site are as follows:
    Site 1
    7
    7
    7
    Mean = 7
    Site 2
    6
    7
    7
    Mean = 6.67
    Site 3
    7
    7
    8
    Mean = 7.33
    Site 4
    7
    8
    8
    Mean = 7.67

    In second season raw data of pH for three sites analysed in triplicate and mean value for site are as follows:
    Site 1
    7
    7
    7
    Mean = 7
    Site 2
    7
    7
    8
    Mean = 7.33
    Site 3
    6
    6
    8
    Mean = 6.67
    When comparing these two seasons using mann whitney u test, should I use all triplicate values (as n = 4 x 3 = 12, for first season and n = 3 x 3 = 9, for second season) or I should use means for four sites in first season (n = 4) and three sites in second season (n = 3). What is correct method?
    Please help me!
    Thanks in advance!!!
    Sk2

  2. #2
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    Re: how to arrange data in Mann - Whitney U test


    The three determinations from any particular site are not independent, so you need to use the means.

  3. The Following User Says Thank You to katxt For This Useful Post:

    sk2 (05-30-2017)

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