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Multiple Choice
Identify the choice that best completes the statement or answers the question.
1. Even if a treatment has no effect, it is still possible to obtain an extreme sample mean that is very different from this population mean. If this happens, you are likely to ____.
a. reject H0 and make a Type I error
b. correctly reject H0
c. fail to reject H0 and make a Type II error
d. correctly fail to reject H0
2. A Type I error is defined as ____.
a. rejecting a false null hypothesis
b. rejecting a true null hypothesis
c. failing to reject a false null hypothesis
d. failing to reject a true null hypothesis
3. A Type II error means that a researcher has ____.
a. concluded that a treatment has an effect when it really does
b. concluded that a treatment has no effect when it really has no effect
c. concluded that a treatment has no effect when it really does
d. concluded that a treatment has an effect when it really has no effect
4. A researcher uses a hypothesis test to evaluate H0 ?= 80. Which combination of factors is most likely to result in rejecting the null hypothesis?
a. M = 85 and ? = .01
b. M = 85 and ? = .05
c. M = 90 and ? = .01
d. M = 90 and ? = .05
5. A population is known to have a mean of ? = 50. A treatment is expected to decrease scores for individuals in this population. If the treatment is evaluated using a one-tailed hypothesis, then the null hypothesis would state ____.
a. ? ? 50
b. ? ? 50
c. ? ? 50
d. ? ? 50
6. A treatment is administered to a sample selected from a population with a mean of ? = 80 and a standard deviation of ? = 10. After treatment, the effect size is measured by computing Cohen's d, and a value of d = 0.60 is obtained. Based on this information, the mean for the treated sample is M = ____.
a. 6
b. 60
c. 86
d. cannot be determined without additional information
7. A sample of n = 9 scores has SS = 72. What is the estimated standard error for the sample mean?
a. 9
b. 3
c. 1
d. cannot answer without knowing the sample mean
8. Which set of sample characteristics is most likely to produce a large value for the estimated standard error?
a. a large sample size and a small sample variance
b. a large sample size and a large sample variance
c. a small sample size and a small sample variance
d. a small sample size and a large sample variance
9. Which set of sample characteristics is most likely to produce a significant t statistic?
a. a large sample size and a small sample variance
b. a large sample size and a large sample variance
c. a small sample size and a small sample variance
d. a small sample size and a large sample variance
10. A sample is selected from a population with ? = 80 and a treatment is administered to the sample. If the sample variance is s2 = 20, which set of sample characteristics is most likely to lead to a decision that there is a significant treatment effect?
a. M = 85 for a sample of n = 25
b. M = 85 for a sample of n = 100
c. M = 90 for a sample of n = 25
d. M = 90 for a sample of n = 100
11. If a researcher reports a t statistic with df = 20, how many individuals were in the sample?
a. n = 19
b. n = 20
c. n = 21
d. cannot be determined from the information given
12. With ? = .01, what is the critical t value for a one-tailed test with n = 30?
a. t = 2.462
b. t = 2.756
c. t = 2.457
d. t = 2.750
13. The results of a hypothesis test are reported as follows: t(29) = 2.70, p ? .05. Based on this report, how many individuals were in the sample?
a. 28
b. 29
c. 30
d. cannot be determined from the information provided
14. In a hypothesis test using a t statistic, what is the influence of using a large sample?
a. A larger sample tends to lower the likelihood of rejecting the null hypothesis.
b. A larger sample tends to increase the likelihood of rejecting the null hypothesis.
c. The size of the variance has no impact on the outcome of the hypothesis test.
d. Cannot determine without more information.
15. As sample variance increases, what happens to measures of effect size such as r2 and Cohen's d?
a. They also tend to increase.
b. They tend to decrease.
c. Sample variance does not have any great influence on measures of effect size.
d. The effect of sample variance depends on other factors such as sample size.
16. An independent-measures study ____.
a. uses a different sample for each of the different treatment conditions being compared
b. uses the same sample for each of the different treatment conditions being compared
c. uses the data from one sample to evaluate a hypothesis about the population mean
d. None of the other choices are correct.
17. The null hypothesis for the independent-measures t test states ____.
a. ?1 ? ?2 = 0
b. M1 ? M2 = 0
c. ?1 ? ?2 ??0
d. M1 ? M2 ? 0
18. An independent-measures experiment uses one sample with n = 6 and a second sample with n = 10 to compare two experimental treatments. The t statistic from this experiment will have degrees of freedom equal to ____.
a. 7
b. 8
c. 14
d. 15
19. One sample of n = 10 scores has a variance of s2 = 6 and a second sample of n = 10 scores has a variance of s2 = 8. The pooled variance for these two samples will be ____.
a. 6
b. 7
c. 8
d. 14
20. Which set of sample characteristics is most likely to produce a significant value for the independent-measures t statistic?
a. a small mean difference and small sample variances
b. a large mean difference and small sample variances
c. a small mean difference and large sample variances
d. a large mean difference and large sample variances
21. What is the estimated standard error for the independent-measures t statistic for the following two samples? Sample 1: n = 4 with SS = 100. Sample 2: n = 8 with SS = 140.
a. 3
b. 9
c. 24
d. 242
22. An independent-measures research study uses two samples, each with n = 8 participants. If the data produce a t statistic of t = 2.10, then which of the following is the correct decision for a two-tailed hypothesis test?
a. Reject the null hypothesis with ? = .05 but fail to reject with ? = .01.
b. Reject the null hypothesis with either ? = .05 or ? = .01.
c. Fail to reject the null hypothesis with either ? = .05 or ? = .01.
d. cannot answer without additional information
23. For an independent-measures research study, the data show a 10-point difference between the two treatment means and a pooled variance of 4. Given this information, the value of Cohen's d is ____.
a. 10/4
b. 10/2
c. 4/10
d. 2/10
24. For which of the following situations would a repeated-measures study be appropriate?
a. comparing attitude scores for males versus females
b. comparing salary levels for college graduates and those who did not graduate from college
c. evaluating the difference in self-esteem between student athletes and non-athletes
d. evaluating the effectiveness of a cholesterol medication by comparing cholesterol levels before and after the medication
25. In a repeated-measures experiment, each individual participates in one treatment condition and then moves on to a second treatment condition. One of the major concerns in this type of study is that participation in the first treatment may influence the participant's score in the second treatment. This problem is called ____.
a. individual differences
b. order effects
c. homogeneity of variance
d. bi-treatment effect
26. For a repeated-measures experiment comparing two treatment conditions, the t statistic has df = 10. How many participants were used in the entire study?
a. 9
b. 22
c. 18
d. 11
27. In general, an increase in the sample size in a repeated-measures study will cause ____.
a. an increase in the standard error and an increase in the value of t
b. an increase in the standard error and a decrease in the value of t
c. a decrease in the standard error and an increase in the value of t
d. a decrease in the standard error and a decrease in the value of t
28. A repeated-measures study finds a mean difference of MD = 5 points between two treatment conditions. Which of the following sample characteristics is most likely to produce a significant t statistic for the hypothesis test?
a. a large sample size (n) and a large variance
b. a large sample size (n) and a small variance
c. a small sample size (n) and a large variance
d. a small sample size (n) and a small variance
29. A major concern with a repeated-measures study is the possibility that ____.
a. you will obtain negative values for the difference scores
b. the results will be influenced by order effects
c. the mean difference is due to individual differences rather than treatment differences
d. All of the other options are major concerns.
30. A repeated-measures study produces a sample mean difference of MD = 4.5 with s2 = 100 for a sample of n = 16 participants. For this study, the estimated value of Cohen's d would be ____.
a. d = 4.5/100 = 0.045
b. d = 4.5/10 = 0.45
c. d = 4.5/2.5 = 1.80
d. The value of d cannot be determined from the information provided.
True/False
Indicate whether the statement is true or false.
31. If the obtained sample mean is not in the critical region, then the correct statistical decision is to fail to reject the null hypothesis.
32. Whenever the statistical decision is to fail to reject the null hypothesis, there is a risk of a Type II error.
33. The value obtained for Cohen's d does not depend on the sample size.
34. The results from an independent-measures t hypothesis test are reported as "t(24) = 3.85, p ? .01, two tailed." For this test, df = 24.
Other
35. Research data indicate that adolescents, especially adolescent girls, experience a drop in self-esteem. To evaluate this result, a researcher obtains a sample of n = 9 adolescent girls, all 13 years old. A self-esteem test is given to each participant and the average score for the sample is M = 66. It is know that the distribution of self-esteem scores for the population of pre-teen girls is normal with ? = 75.
a. Assuming that the population standard deviation is ? = 12, is this result sufficient to conclude that self-esteem for adolescent girls is significantly different from self-esteem for pre-teen girls? Use a two-tailed test with ? = .05.
b. If ? = 24, is the result sufficient to conclude that there is a significant difference?
c. Explain why the two tests lead to different outcomes.
36. A researcher is testing the effect of a new cold and flu medication on reaction time. A sample of n = 9 students is obtained and each student is given the normal dose of the medicine. Thirty minutes later, each student's reaction time is measured. The scores for the sample averaged M = 211 milliseconds with SS = 1152.
a. Assuming that reaction time for students in the regular population averages ? = 200 milliseconds, are the data sufficient to conclude that the medication has a significant effect on reaction time? Test at the .05 level of significance.
b. Compute r2, the percentage of variance explained by the treatment effect.
37. A sample of freshmen takes a reading comprehension test and their scores are summarized below. If the mean for the general population on this test is ? = 12, can you conclude that this sample is significantly different from the population. Test with ? = .05.
Sample Scores: 16, 8, 8, 6, 9, 11, 13, 9, 10
38. A biopsychologist studies the role of the brain chemical serotonin in aggression. One sample of rats serves as a control group and receives a placebo. A second sample of rats receives a drug that lowers brain levels of serotonin. Then the researcher tests the animals by recording the number of aggressive responses each of the rats display. The data are presented below.
a. Does the drug have a significant effect on aggression? Use an alpha level of .05, two tails.
b. Use Cohen's d to measure the effect size.
Low Serotonin Control
n = 4 n = 8
M = 22 M = 14
SS = 76 SS = 164
39. The following data were obtained from an independent measures study. Determine if there is a significant difference between the treatments. Use ? = .01
Treatment 1 Treatment 2
5 6
1 10
2 14
3 12
4 18
40. A teacher gives a third grade class of n = 16 a reading skills test at the beginning of the school year. To evaluate the changes that occur during the year, students are tested again at the end of the year. Their test scores revealed an average improvement of MD = 4.7 points.
a. If the variance for the difference scores is s2 = 144, are the results sufficient to conclude that there is significant improvement? Use a one-tailed test with ? = .05.
b. If the variance for the difference scores is reduced to s2 = 64, are the results sufficient to conclude that there is significant improvement? Use a one-tailed test with ? = .05.
c. Describe the effect on reducing the variance of the difference scores.
Solution Description

**MULTIPLE CHOICE**

1. ANS: A REF: p. 200

2. ANS: B REF: p. 199

3. ANS: C REF: p. 200

4. ANS: D REF: p. 207

5. ANS: A REF: p. 213

6. ANS: C REF: p. 217

7. ANS: C REF: p. 234

8. ANS: D REF: p. 246

9. ANS: A REF: p. 246

10. ANS: D REF: p. 246