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Experiments: Part 3.

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Presentation on theme: "Experiments: Part 3."— Presentation transcript:

1 Experiments: Part 3

2 Overview How do the main types of validity apply to experimental research? What are some of the main threats to internal validity? What confusing concepts would you like to review before Exam 2?

3 Validity in Experiments
Measurement validity Statistical conclusion validity External validity Internal validity

4 Threats to Internal Validity
Something other than the experimental manipulation differs between groups and drives observed differences in the dependent variable Imbalance History threat vs. maturation threat Testing threat vs. instrumentation threat Regression toward the mean Mortality (attrition, dropout)

5 Regression toward the Mean
Non-experiment: Pre-post within-subject design

6 Experimental design

7 Mortality

8

9 Selection Bias 87% % % % Mortality


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