11.1 What factor determines whether you should use a z-test or a t-test statistic for a hypothesis test?

11.2 A sample is selected from a population mean of = 30. A treatment is administered to the individuals in the sample and, after treatment, the sample mean found to be M = 31.3 with a sample variance of s2 = 12. a. If the sample consists of n = 16 individuals, are the data sufficient to conclude that there is a significant treatment effect using a two-tailed test with = .05? b. If the sample consists of n = 36 individuals, are the data sufficient to conclude that there is a significant treatment effect using a two-tailed test with = .05?

11.3 Ackerman & Goldsmith (2011) found that students who studied text from printed hard copy had better test scores than students who studied text presented on a screen. In a related study, a professor noticed that several students in a large class had purchased the e-book version of the course textbook. For the final exam, the overall average for the entire class was = 85, but the n = 10 students who purchased the e-book had a mean of M = 77 with a standard deviation of s = 7. Do these data indicate a significant decrease in test scores on the final exam due to the use of a e-book? Use a one-tailed test with = .05.

11.4 Oishi & Shigehiro (2010) report that people who move from home to home frequently as children tend to have lower than average levels of well-being as adults. To further examine this relationship, a psychologist obtains a sample of n = 12 young adults who each experienced 5 or more different homes before they were 16 years old. These participants were given a standardized well-being questionnaire for which the general population has an average score of = 40. The well-being scores for this sample are as follows: 23, 37, 41, 35, 43, 37, 33, 34, 36, 38, 31, 38. On the basis of this sample, is well-being for frequent movers significantly different from the well-being of the general population? Test with alpha = .05. Is this a one- tailed or two-tailed test?

Note for problems 11.2-11.4 above: Be sure and show a full diagram of the research design. Also show all steps and calculations you made for each test following the process outlined in the t-test formula sheet handout. What statistical decision do you make in each case.