1. Although there is a popular belief that herbal remedies such as Ginkgo biloba and Ginseng may improve learning and memory in healthy adults, these effects are usually not supported by well controlled research (Persson, Bringlov, Nilsson, and Nyberg, 2004). In a typical study, a researcher obtains a sample of n = 16 participants and has each person take the herbal supplements every day for 90 days. At the end of the 90 days, each person takes a standardized memory test. For the general population, scores from the test form a normal distribution with a mean of = 50 and a standard deviation of = 12. The sample of research participants had an average of M = 54. a. Assuming a two-tailed test, state the null hypothesis in a sentence that includes the two variables being examined. b. Using the standard 4-step procedure, conduct a two-tailed hypothesis test with = .05 to evaluate the effect of the supplements.

2. Babcock and Marks (2010) reviewed survey data from 2003-2005, and obtained an average of = 14 hours per week spent studying by full-time students at 4-year colleges in the United States. To determine whether this average has changed in the past 10 years, researcher selected a sample of n = 64 of today's college students and obtained an average of M = 12.5 hours. If the standard deviation for the distribution is = 4.8 hours per week, does this sample indicate a significant change in the number of hours spent studying? Use a two-tailed test with = .05.

3. The psychology department is gradually changing its curriculum by increasing the number of online course offerings. To evaluate the effectiveness of this change, a random sample of n = 36 students who registered for Introductory Psychology is placed in the online version of the course. At the end of the semester, all students take the same final exam. The average score for the sample is M = 76. For the general population of students taking the traditional lecture class, the final exam scores form a normal distribution with a mean of = 71. a. If the final exam scores for the population have a standard deviation of = 12, does the sample provide enough evidence to conclude that the new online course is significantly different from the traditional class? Use a twotailed test with = .05. b. If the population standard deviation is = 18, is the sample sufficient to demonstrate a significant difference? Again, use a two-tailed test with = .05. c. Comparing your answers for parts a and b, explain how the magnitude of the standard deviation influences the outcome of a hypothesis test.

4. A random sample is selected from a normal population with a mean of = 30 and a standard deviation of = 8. After a treatment is administered to the individuals in the sample, the sample mean is found to be M = 33. a. If the sample consists of n = 16 scores, is the sample mean sufficient to conclude that the treatment has a significant effect? Use a two-tailed test with = .05. b. If the sample consists of n = 64 scores, is the sample mean sufficient to conclude that the treatment has a significant effect? Use a two-tailed test with = .05.

5. The researchers cited in the previous problem (Liguori and Robinson, 2001) also examined the effect of caffeine on response time in the driving simulator. In a similar study, researchers measured reaction time 30 minutes after participants consumed one 6-ounce cup of coffee. Using the same driving simulation task, for which the distribution of reaction times is normal with = 400 msec and = 40, they obtained a mean of M = 392 for a sample of n = 36 participants. a. Are the data sufficient to conclude that caffeine has a significant effect on reaction time? Use a two tailed test with = .05.