January 29, 2008 Lecture Notes

January 29, 2008 Lecture Notes - January 29, 2008 Internal...

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January 29, 2008 Internal Validity~ -Internal Validity - the extent to which we are certain that the IV caused the differences found on the DV - 3 basic conditions : 1) Co-variation : there is relationship between the IV and the DV 2) Temporal Precedence : the cause must precede the effect. (The IV occurs before the DV) 3) No plausible alternative explanations a. Confound : some other variables (not IV) could explain the results of the study -How can we eliminate (or minimize) these alternative explanations? (and thereby increase the internal validity of our study?) 1) Holding conditions constant: try to keep everything exactly the same except for the IV 2) Balancing the individual differences (or characteristics) of the participants in different conditions -How do we balance (or account for) individual differences? 1) Random assignment to condition 2) Repeated measures design Factors Affecting Internal Validity - Maturation : changes in DV that occur due to normal maturation or session effects (ex: getting
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