Question

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 = 28 college students. Each student is given a ginkgo biloba supplement daily for 6 weeks and then all of the participants are given a standardized memory test. Scores on the standardized test are μ = 80 and standard deviation of 15. The sample of 28 students had a mean score of M = 85. (8 points) Do the data indicate a significant effect of the herb on memory? Use a two-tailed test with α = 0.05. (Show all steps.) Compute Cohen's d to measure the size of the effect IF it exists. Write a sentence describing the outcome of the hypothesis test as it would appear in a research report.

Answer 1

H₀: = 80

H₁: 80

The test statistic z = (M - )/()  

= (85 - 80)/(15/)

= 1.76

P-value = 2 * P(Z > 1.76)

= 2 * (1 - P(Z < 1.76))

= 2 * (1 - 0.9608)

= 2 * 0.0392 = 0.0784

Since the p-value is greater than the significance level (0.0784 > 0.05), so we should not reject the null hypothesis.

There is not sufficient evidence to conclude that there is significant effect of the herb on memory.

Cohen's d = (M - )/

= (85 - 80)/15 = 0.33