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Chapter 9 Procedure for Conducting an Experiment

Chapter 9 Procedure for Conducting an Experiment. Power – probability of rejecting a false null hypothesis. Probability of detecting a difference between conditions when one exists. We want high power in our study. Approx 0.8 What does Power of 0.8 mean?.

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Chapter 9 Procedure for Conducting an Experiment

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  1. Chapter 9 Procedure for Conducting an Experiment ch12(1)

  2. Power – probability of rejecting a false null hypothesis. Probability of detecting a difference between conditions when one exists. We want high power in our study. Approx 0.8 What does Power of 0.8 mean? ch12(1)

  3. Effect Size– Correlation between IV and DV. Tells you how well you can predict the DV, if you know the participant’s IV condition. e.g., If I know whether a person is male or female, how much does that improve my ability to predict their math ability. Cohen’s (1992) Criteria. Effect size or .10 is small, .30 is moderate and .50 is large. ch12(1)

  4. The larger the Effect Size is the more Power the study has. • Very Powerful studies can find significant (not due to chance) effects that are very small. • Studies with low power may be unable to detect even large effects of the IV ch12(1)

  5. Alpha Level: Chance we are willing to take off making a Type I error. If we change alpha to .10, we would correctly accept a lot more comparisons as significant, but we will also greatly increase our chance of making a type one error. ch12(1)

  6. Sample Size, Power and Effect Size are Related in such a way that if you know two of these values for a study, you can Determine the third (from a chart) for a given alpha level. ch12(1)

  7. ↑ Sample Size ↑ Power ↑ Effect Size ↑ Power ↑ Alpha ↑ Power ch12(1)

  8. Apparatus and /Instructions ch12(1)

  9. Procedure Instructions (Protocol) All subjects receive the same instructions with the exception of changes needed to manipulate the IV. Scheduling Participants. Time of Day Interactions Running in Groups or Individually ch12(1)

  10. Pilot Studies - tests the procedure - wording or the instructions - practice for the experimenter - run through for equipment and computer programs ch12(1)

  11. Debriefing (Post experimental Interview) Functions • Ethical - undo deception - undo stress • Educational Function • Post experimental Inquiry • Satisfaction ch12(1)

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