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.