2. SOC101Y University of Toronto 2013-14 Robert Brym Online Mini-Lecture #7 Establishing Causality in Experimental and Nonexperimental Research Click icon to repeat audio Right cursor to advance ->

3. 1 Recruit subjects 2 Randomly assign them* 3 Experimental group** 3 Control group*** 4 Measure dependent variable**** (hypothesized effect) in experimental and control groups 5 Expose experimental group to independent variable (hypothesized cause) 5 Do not expose control group to independent variable * Randomization involves assigning individuals to groups by chance processes. 6 Re-measure dependent variable in experimental and control groups to determine the degree to which it has changed ** The experimental group is the group exposed to the independent variable (hypothesized cause). *** The control group is the group not exposed to the independent variable. **** The dependent variable is the hypothesized effect. Click icon to repeat audio Right cursor to advance ->

4. Turning a Classroom into a Contingency Table (a cross-classification of cases by at least two variables) BACK LEFT FRONT RIGHT no act of physical violence in the past year 1+ act(s) of physical violence in the past year Click icon to repeat audio Right cursor to advance ->

5. no act of physical violence per year and more than 10 hours TV per week at least 1 act of physical violence per year and 10 or fewer hours TV per week no act of physical violence per year and 10 or fewer hours TV per week Turning a Classroom into a Contingency Table (a cross-classification of cases by at least two variables) at least 1 act of physical violence per year and more than 10 hours TV per week BACK LEFT FRONT RIGHT Click icon to repeat audio Right cursor to advance ->

6. TV Viewing by Aggressiveness (in percent) Measures strength of association Number of cases in each column Percent of cases in each column Percent of cases in each column that fall into a category of each row variable. Note the direction in which the table is percentaged. C O L ROW U M N Click icon to repeat audio Right cursor to advance -> A B C D E F

7. TV Viewing by Aggressiveness (men only) Click icon to repeat audio Right cursor to advance ->

8. Testing an Association forSpuriousness (1) We believe there is a causal relationship between TV viewing and aggressiveness: TV viewing Aggressiveness (independent variable)(dependent variable) (2) By controlling for gender we can see whether gender has created a spurious association between TV viewing and aggressiveness: TV viewing (independent variable) Respondent’s gender (control variable) aggressiveness (dependent variable) (association) (no association) Click icon to repeat audio Right cursor to advance ->

9. Summary  In both experimental and nonexperimental research, we are interested in determining whether relationships between variables are causal or spurious. To do so, we must remove the effects of extraneous or irrelevant variables that may “contaminate” the observed relationship.  In experimental research, we remove the effect of extraneous variables by randomizing the allocation of subjects to experimental and control groups and repeating experiments many times.  In nonexperimental research, we remove the effect of extraneous variables by controlling for variables that we expect may be irrelevant. Click icon to repeat audio