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Unformatted text preview: 2-8-11Extraneous Variables (Confounders)oDifference between groups can cause the distributions to be closer together or farther apart; This can be the result of the IV or the EVoNo way to tell which caused the differenceoExtraneous Variable (EV) – uncontrolled variables that can cause unintended changes between groupsoConfounded – when you don’t know whether the IV or the EV caused the differenceoBook example: Reading ComprehensionoStandard method of teaching used with 1stgraders and the New method is used with the 2ndgraders. We find a difference between the two groups. What is the EV in this example? Grade levelo(Diagram in book)oDifference between two groups with no confounder operatingoDifference between two….o……Nuisance Variables vs. Extraneous VariablesoExample 1oIV: list of words with no slow synonyms; List of words only slow synonymsoDV: Reaction timeoNV: Age of all participants in both conditions is random mix of 12-78 yr oldsoEV: age could be alternate explanation for the difference if one group is all senior citizens and other college studentsoExample 2oIV: words flash on screen count letters; words flash on screen put them in sentenceoDV: recall a list of wordsoNV: The elevator goes off randomly when people ride I during both...
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- Spring '11
- Juan, Nancy, Cola B, different treatment sequences