ben mccarthy

31. Some researchers claim that herbal supplements such as ginseng or ginkgo biloba enhance human memory. To test this claim, a researcher selects a sample of n = 25 college students. Each student is given a ginkgo biloba supplement daily for six weeks and then all the participants are given a standardized memory test. For the population, scores on the test are normally distributed with  = 70 and  = 15. The sample of n = 25 students had a mean score of M = 75.

a. Are the data sufficient to that the herb has a significant effect on memory? Use a two-tailed test with  = .05.

b. Compute Cohen’s d for this study.

32. A sample of n = 9 participants is obtained from a population with  = 29, and a treatment is administered to the individuals in the sample. After treatment, the scores for the nine participants are as follows: 23, 33, 26, 28, 30, 26, 27, 25, 25.

a. Are the data sufficient to conclude that the treatment has a significant effect? Use a two-tailed test with  = .05.

b. Are the data sufficient to conclude that the treatment significantly decreased scores? Use a one-tailed test with  = .05.

33. The following data are from an independent-measures experiment comparing two treatment conditions:

Treatment 1 Treatment 2

6	19
13	9
8	18
4	10
13	12
4	14
11	19
5	11

a. Do these data indicate a significant difference between the treatments at the .05 level of significance?

b. Compute r2 to measure the size of the treatment effect.

c. Write a sentence demonstrating how the outcome of the hypothesis test and the measure of effect size would appear in a research report.

34. For the following data from a repeated-measures study:

a. Find the difference scores

b. Calculate MD and the variance for the difference scores

c. Calculate the estimated standard error for the mean difference

Subject

Subject	Treatment 1	Treatment 2
A	12	14
B	6	16
C	8	10
D	9	11