A school counselor tests the level of depression in fourth graders in a particular class of 20 students. The counselor wants to know whether the kind of students in this class differs from that of fourth graders in general at her school. On the test, a score of 10 indicates severe depression, while a score of 0 indicates no depression. From reports, she is able to find out about past testing. Fourth graders at her school usually score 5 on the scale, but the variation is not known. Her sample of 20 fifth graders has a mean depression score of 4.4. Use the .01 level of significance.
1. The counselor calculates the unbiased estimate of the population's variance to be 15. What is the variance of the distribution of means?
A) 15/20 = 0.75
B) 15/19 = 0.79
C) 152/20 = 11.25
D) 152/19 = 11.84
2. Suppose the counselor tested the null hypothesis that fourth graders in this class were less depressed than those at the school generally. She figures her t score to be -.20. What decision should she make regarding the null hypothesis?
A) Reject it
B) Fail to reject it
C) Postpone any decisions until a more conclusive study could be conducted
D) There is not enough information given to make a decision
3. Suppose the standard deviation she figures (the square root of the unbiased estimate of the population variance) is .85. What is the effect size?
A) 5/.85 = 5.88
B) .85/5 = .17
C) (5 - 4.4)/.85 = .71
D) .85/(5 - 4.4) = 1.42

Note that for us to be able to get the answer in question one, we have to divide the unbiased estimate for the population variance by the use of 20 so that we can be able to get our unbiased estimate for the variance: And as such;

15/20 = 0.75.

The term fail to reject implies that the null hypothesis is one that has not been disproven or wrong and therefore the use of the term "failure to reject." It is one that should not be taken with acceptance.

Therefore, 1. The variance of the distribution of means option A) 15/20 = 0.75

2. The decision that counselor should make regarding the null hypothesis is that: option "Fail to reject it"

3. The effect of the size is: option c: (5 − 4.4)/.85 = .71

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