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