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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 μ = 70 and σ = 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 α = .05.

b.  Compute Cohen’s d for this study.

32.A sample of n = 9 participants is obtained from a population with μ = 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 α = .05.

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

33.The following data are from an independent-measures experiment comparing two treatment conditions:                  Treatment 1     Treatment 2

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 M_D and the variance for the difference scores

c.  Calculate the estimated standard error for the mean difference