PSYA01H3 Chapter Notes - Chapter 2: Internal Validity, Akira Haraguchi, Case Method
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Self-selection a problem that occurs when anything about a person determines whether he or she will be included in the experimental or control group. Random assignment a procedure that uses a random event to assign people to the experiment or control group: solves the problem of self-selection. In the diagram below: children with adult supervision are shown in orange and those without adult supervision are shown in blue. The independent variable is exposure to media violence and the dependent variable is aggression. Random assignment ensures that participants in the experimental and the control groups are on average equal in terms of all possible third variables. In essence, it ensures that there is no correlation between a third variable and the dependent variable. Random assignment is a powerful tool, but it doesn"t work every time you use it. We could expect the two groups to have roughly equal numbers but this does not happen sometimes.
