Mann Whitney U Test by djd18436

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									                                   Mann Whitney U Test
Problem
       Two teachers studied whether students would generalize learned Imitation when placed
in a new situation. Five students were taught to imitate a leader; four students received no
training. The teachers compared the number of trials needed to reach criterion.




Hypothesis

Ho: There is no difference in the number of trials to each criterion for the two groups
of students.




Statistical Test: The Mann-Whitney U Test Is chosen because the study uses two independent

samples, uses small samples, and uses measurement at the ordinal level.




Data
          E Students’ Trials                     C Students’ Trials
                 78                                    110
                 64                                     70
                 75                                     53
                 45                                      51
                  82




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                                       Mann Whitney U Test
Step 1: Label each test paper either E, for experimental group, or C, for
        control group. If neither group is really experimental, call the group
        that you expect to get higher scores the E group. See how many pupils are
        in the smaller group. In our example the control group is smaller, and
        N1=7.
        The experimental group has eight pupils, no N2 = 8.



Step 2: Put the papers in numerical order based on the test scores.


Step 3: Give the paper with the lowest score a rank of one, next-lowest a rank
        of two, and so on. The highest score will have the highest rank.


Step 4: Make up a list like Table 1, that is, list rank (in order) in Row A and
        indicate for each paper whether subject is in the experimental (E) or
        control (C) group in Row B.


Step 5: Our next step is to count the number of E scores that are lower than
        each C score and write this number below the C score. The first C
        score is the lowest, so there are no E scores below it. Thus you write
        “0” under this score. The next C score (rank 3) has one E score below
        it, so write “1” under the C score. The next C score (rank 4) also has one E score
        below it, so again enter “1.” Go ahead and work out the rest of numbers
        in Row C and see if your numbers agree with those given in Table 1.


Step 6: Add up the numbers in Row C. The total, which is called U, is 16.


Table 1: Reading ranks of 15 first-grade pupils________________________________

Row____________________________________________________________________________

A.Rank:       1    2   3   4   5   6     7    8   9   10     11   12 13 14 15

B.Group:      C   E    C   C   E   C      E   C   E   C       E   C   E   E   E

C.U Score:    0        1   1       2          3       4           5




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