1. How does one design an experiment and analyze the resulting data?
Illustrative example:
“Does viewing violence increase aggression?”
Designing the experiment:
Internal and external validity
Controlling for error
Summarizing the obtained data:
Central tendency and variability
Calculating a “test statistic” (Z)
Interpreting the value Z

2. Research design terminology (from last week):
Independent variable
Dependent variable
Systematic (confounding) error
Unsystematic (random) error
“Holding constant”
Randomization
Controlling for subject expectations:
e.g. placebo control
Controlling for experimenter expectations:
e.g. double-blind control

3. Summary of hypothetical results from a correlational study relating amount of violent TV viewing and degree of “manifest aggressiveness” (shown earlier):
Degree of “manifest aggressiveness”
r > 0
Amount of violent TV viewing

4. Independent Variable:
Research hypothesis:
“Watching violent TV provokes aggression.”
Experimental group
Control group
Independent Variable:
Exposure to the experimental condition
Exposure to the control condition
Dependent variable:
Performance
Performance
Is the difference statistically significant?

5. Graphical summary of data
Violent
Nonviolent
Type of TV segment
Mean seconds on “hurt” button 12 10 8 6 4 2
Girls
Boys

6. (The 68 Girls) Experimental Control X (X-M)2 1. 11.0 5.76 1. 6.0 0.16
5.76
0.16
13.69 .
1.40 X X

7. Numerical and Graphical Summary of Data from the 68 Girls:
Mean:
Variance:
S.D.:
Experimental group (N=34)
Control group (N=34) 10 8 6 4 2
Mean seconds on “hurt” button
Violent
Nonviolent

8. Calculating Z from the data: (Z is the test statistic.)?

9. Normal distribution of Z:
.05
+1.65
(critical value of Z) Z