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Making Inferences about Causality

+. Watching violent TV. Acting violent. Making Inferences about Causality. In general, children who watch violent television programs tend to behave more aggressively toward their peers and siblings. Question: Can we assume a causal relationship between these two variables?.

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Making Inferences about Causality

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  1. + Watching violent TV Acting violent Making Inferences about Causality • In general, children who watch violent television programs tend to behave more aggressively toward their peers and siblings. • Question: Can we assume a causal relationship between these two variables?

  2. Making Inferences about Causality • Answer: not necessarily • Although causality generally implies correlation, correlation does not necessarily imply causality. • There are at least three other ways to explain the correlation between TV viewing and aggressive behavior.

  3. + Watching violent TV Acting violent Making Inferences about Causality (1) Acting aggressively makes you want to watch more violent TV.

  4. + + Watching violent TV Acting violent Making Inferences about Causality (2) Acting violent makes you want to watch more TV and watching TV makes you act more violently.

  5. + + Watching violent TV Living in a violent family Acting violent Making Inferences about Causality (3) A “third variable” influences both variables, causing them to be correlated.

  6. How can we tease apart these various possibilities? • One way to do so is to conduct an experiment • In an experiment, at least one variable is manipulated (i.e., systematically varied) by the researcher in order to study its effects on another variable.

  7. + Watching violent TV Acting violent Experimental Research • Features of an experiment (a) At least one variable is manipulated or varied by the experimenter: independent variable (IV) (b) The variable presumably affected by the manipulation is called the dependent variable (DV) (c) random assignment to conditions IV DV

  8. Dependent Variable: Aggressive behavior Number of times the child punches his or her peers on the playground IV DV • Independent Variable: Watching violent TV • Levels: • view an episode of the Sopranos • view an episode of the Sopranos in which the violent scenes have been edited

  9. Confounding Variable • Confounding variable: a variable that influences the dependent variable and is associated with the independent variable • When confounding variables are present, we cannot make a strong inference that the independent variable causes the dependent variable.

  10. Random Assignment • Why is random assignment important? • Consider what would happen if we assigned men to the “violent” level of the IV and women to the “non-violent” level of the IV. • Sex would be correlated with the IV.

  11. Random Assignment • Random assignment to conditions helps to remove the problem of confounding variables. • When people are randomly assigned to conditions, we should (in the long run) have equal numbers of men and women in our two conditions. • As a result, the possible confound (e.g., sex) is uncorrelated with the independent variable.

  12. Random Assignment • Previously, we had discussed the possibility that the violence of the family context is a “third variable” that might be causing both violent TV viewing and aggressive behavior. • We could control for this possible confound by randomly assigning people to violent TV viewing conditions. • Theoretically, there should be an equal number of people from violent families in each condition.

  13. Confounding Variables and Non-Confounding Variables • A variable can exist that has a genuine effect on the dependent variable but that is uncorrelated with the independent variable.

  14. Acting violent + + + + Living in a violent family Living in a violent family Watching violent TV Watching violent TV Acting violent Confounding Variables and Non-confounding Variables Confounding Non-Confounding

  15. Experimental Research • Between- and within-subjects designs between-subjects: different people are exposed to each level of the IV within-subjects: the same people exposed to each level of the IV

  16. Experimental Research • Pros and cons of between and within designs • between: different people in each condition. They may differ in certain respects • within: same DV assessed many times. Problems with learning effects and awareness of the manipulation • counter-balancing: balancing the order of conditions.

  17. Counter-balancing t1 t2 t3 Person 1 C1 C2 C3 Person 2 C1 C3 C2 Person 3 C2 C1 C3 Person 4 C2 C3 C1 Person 5 C3 C1 C2 Person 6 C3 C2 C1

  18. Counter-balancing t1 t2 t3 Group 1 C1 C2 C3 Group 2 C1 C3 C2 Group 3 C2 C1 C3 Group 4 C2 C3 C1 Group 5 C3 C1 C2 Group 6 C3 C2 C1

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