PSY 429 Experimental Psychology
Class Exercise #10
Power and Strength of Association Tests
PSY 429 Experimental Psychology
Class Exercise #10
Power and Strength of Association Tests
1. If someone asks you, "What level of power did you achieve in your study?" and you answer, "Power turned out to be .90," what did the question refer to and what does your answer mean?
2. What four factors affect the power of a statistical test?
3. What does the eta-squared statistic reflect? (don't just say the strength of association between IV and DV).
4. Translate into words what an eta-squared of .65 means.
5. The following experiment measured manual dexerity in four participants over a series of three practice sessions. The goal of the experiment was to examine changes in manual dexerity performance as a function of practice. Results showed the following sum of squares (SS):
SS-treatment = 14.0
SS-error = 6.0
SS-subjects = 12.0
SS-total = 32.0
What is the strength of association between the IV and the DV and describe what this means.
6. Based on question #5 above, what is the level of power with an alpha level of .05 (assume an equal number of participants in each group)?
7. A school psychologist would like to test the effectiveness of a behavior-modification technique in controlling classroom outbursts of unruly children. A teacher is instructed to use the response-cost technique. Every time a child disrupts the class, he or she is told that the behavior has cost him or her 10 minutes of free time. That is, the free-time period is shortened for each unruly act. For a sample of n = 4 children, the number of outbursts is measured for a day before the treatment is initiated and again 1 week, 1 month, and 6 months after the response-cost technique began.
Results showed the following sum of squares (SS):
SS-treatment = 77.0
SS-error = 11.0
SS-subjects = 13.0
SS-total = 101.0
a. What is the F ratio?b. Is there a significant difference?
c. Conduct a strength of association test using eta-squared and describe in words what this means.
d. Determine the level of power and describe in words what this means.
8. It has been suggested that pupil size increases during emotional arousal. A researcher would therefore like to see if the increase in pupil size is a function of the type of arousal (pleasant versus aversive). A random sample of five subjects is selected for the study. Each subject views all three stimuli: neutral, pleasant, and aversive photographs. The neutral photograph portrays a plain brick building. The pleasant photograph consists of a young man and woman sharing a large lic cream cone. Finally, the aversive stimulus is a graphic photograph of an automobile accident. Upon viewing each stimulus, the pupil size is measured (in millimeters) with sophisticated equipment. The results show the following sum of squares (SS):
SS-treatment = 30.0
SS-error = 28.0
SS-subjects = 6.0
SS-total = 64.0
a. What is the F ratio?b. Is there a significant difference?
c. Conduct a strength of association test using eta-squared and describe in words what this means.
d. Determine the level of power and describe in words what this means.
To go back to Dr. Ryan's Home Page, click on kitty.
Celtic
Clip Art - http://artinfo@aon-celtic.com