Psychological Statistics

Assignment 2: Conducting a z-Test

A researcher predicts that watching a film on institutionalization will change students’ attitudes about chronically mentally ill patients. The researcher randomly selects a class of 36 students, shows them the film, and gives them a questionnaire about their attitudes. The mean score on the questionnaire for these 36 students is 70. The score for a similar class of students who did not see the film is 75. The standard deviation is 12. Using the five steps of hypothesis testing and the 5% significance level (i.e. alpha = .05), does showing the film change students’ attitudes towards the chronically mentally ill?

1. What does it mean to set alpha at .05?
2. What is your null hypothesis? Alternate hypothesis?
3. Is this a one-tailed or two-tailed hypothesis?
4. What is the critical z?
5. Suppose the obtained z was -2.5. Do you reject or fail to reject the null hypothesis?
6. State in words what you have found.