Question 1

Both the Mann-Whitney U test and the Kruskal-Wallis test analyze differences between sums of ranks.

Accepted Answer

Both tests compare the sums of ranks between groups to analyze differences. The Mann-Whitney U test compares the sum of ranks between two independent groups, while the Kruskal-Wallis test compares the sum of ranks among three or more independent groups.

Question 2

The proper use of the Wilcoxin signed ranks test requires that both the raw scores and the difference between the raw scores be of at least ordinal scaling.

Accepted Answer

The Wilcoxin signed ranks test is a non-parametric test that requires the data to be at least of an ordinal scale. This includes both the raw scores and the differences between them. Therefore, the statement is true.

Question 3

Define marginals.

Accepted Answer

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Question 4

If T _obt ≥ T _crit , reject H₀ .

Accepted Answer

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Question 5

The Kruskal-Wallis test analyzes the difference between sample means.

Accepted Answer

The Kruskal-Wallis test analyzes the difference between sample medians, not means.

Question 6

Define expected frequency ( f_e ).

Accepted Answer

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Question 7

Define contingency table.

Accepted Answer

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Question 8

Define chi-square (  ).

Accepted Answer

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Question 9

The Kruskal-Wallis test is used with a correlated groups design.

Accepted Answer

The Kruskal-Wallis test is used with an independent groups design. For correlated groups, the Friedman test is used.

Question 10

When using the Wilcoxin signed ranks test, if the raw scores are tied, the scores are disregarded and N is reduced by 1.

Accepted Answer

The Wilcoxon signed ranks test ranks the differences between paired observations and uses the sign of the difference to determine the direction of the rank. In cases where the raw scores are tied, the tied ranks are averaged and assigned the average rank. This does not affect the size of the sample, so N would not be reduced by 1.

Question 11

If the ranking has been done correctly for the Wilcoxin signed ranks test, the sum of the unsigned ranks should equal n ( n +1)/2.

Accepted Answer

This is true because in the Wilcoxon signed rank test, the positive ranks are summed together and the negative ranks are summed together. By assigning ranks based on the absolute value of the differences between the paired observations, the sum of the ranks will always equal n(n+1)/2.

Question 12

The sign test is less powerful than the Wilcoxin signed ranks test.

Accepted Answer

This is true. The sign test is a non-parametric test that only takes into account the direction of the difference between two related samples, while the Wilcoxin signed ranks test not only takes direction into account but also the magnitude of the difference. As a result, the Wilcoxin test is generally more powerful than the sign test.

Question 13

Both the c 2 test and the Wilcoxin signed ranks test are one-tailed tests.

Accepted Answer

Both the t-test and Wilcoxon signed rank test can be one-tailed or two-tailed tests depending on the research question and hypothesis being tested.

Question 14

Define Mann-Whitney U test.

Accepted Answer

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Question 15

To use the Mann-Whitney U test, n 1 must equal n 2 .

Accepted Answer

The Mann-Whitney U test can be used when the sample sizes for the two groups being compared are different.

Question 16

In an independent groups experiment involving two groups, if chance alone were operating one would expect a great deal of overlap between the two sets of scores.

Accepted Answer

If chance alone were operating, the two groups would not be significantly different from each other, and thus there would be a great deal of overlap between the scores of the two groups.

Question 17

Define Kruskal-Wallis test.

Accepted Answer

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Question 18

Define degree of separation.

Accepted Answer

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Question 19

The Mann-Whitney U test tests the difference between sample means.

Accepted Answer

The Mann-Whitney U test tests the difference between sample medians, not means.

Question 20

Even though for a given experiment U _obt and U ?2'_obt have different values, they still indicate the same degree of separation.

Accepted Answer

The subscript values (S, U, B) may differ, but as long as the values of U and B are the same in both scenarios, they indicate the same degree of separation.

Quiz 17: Chi-Square and Other Nonparametric Tests