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

9. Selection Bias
87% % % %
Mortality