Statistics in Psychology
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 people in general on this questionnaire is 75, with a standard deviation of 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. Calculate the obtained z. Do you reject or fail to reject the null hypothesis?
6. State in words what you have found
- What does it mean to set alpha at .05?
The significance level, sometimes referred to as alpha (α), refers to the probability that the null hypothesis will be rejected if such a hypothesis is true (Haslam & McGarty, 2014). In this case, the 5 percent significance level (α=0.05) is an indication of a 5% risk of establishing a conclusion that there is a difference when an actual difference does not exist.
- What is your null hypothesis? Alternate hypothesis?
Null hypothesis, H0:
Students who watch the film on institutionalization do not change their attitudes towards chronically mentally ill persons.
Alternative hypothesis, Ha:
Students who watch the film on institutionalization will change their attitudes towards chronically mentally ill persons.
- Is this a one-tailed or two-tailed hypothesis?
This is a two-tailed hypothesis considering the fact that it wishes to establish if there is a relationship between the variables of watching institutionalized film and changing attitudes towards mentally ill persons. As such, the test tests for an effect towards either direction.
- What is the critical z?
The critical value of z refers to the area beneath the standard normal model (Aron, Aron, & Coups, 2012). These values can give you the probability of any variables.
- Calculate the obtained z. Do you reject or fail to reject the null hypothesis?
1 – 0.05 = 0.95
Given that it is a two-tail test:
Then, 0.95/2 = 0.475
z-table reading: horizontal reading = 1.9, and vertical reading = 0.6
Summation = 1.9 + 0.6 = 1.96
thus, the critical z value in this case is ±1.96.
since it is a two tailed test, the p value = .4750 x 2 = .9500
z score = 1.64
Since 1.64 does not lie is the rejection region, they we accept the null hypothesis.
- State in words what you have found
According to the
findings, one can conclude that subjecting the students to the
institutionalization film may not necessarily change their attitudes towards
chronically mentally ill persons.
Aron, A., Aron, E. N., & Coups, E. (2012). Statistics for Psychology. Upper Saddle River, NJ: Pearson Education.
Haslam, S. A., & McGarty, C. (2014). Research Methods and Statistics in Psychology. Los Angeles: SAGE.