# Experiment Design 2: Validity - PowerPoint PPT Presentation

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Experiment Design 2: Validity. Martin Ch 2. Demonstration: how to design a bad experiment. How can we measure intelligence?. Conclusion validity. Statistical Appropriate statistics? Internal Really the cause? Construct (Measure) Measure what it is supposed to measure? External

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Experiment Design 2: Validity

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## Experiment Design 2:Validity

Martin Ch 2

### Demonstration: how to design a bad experiment

• How can we measure intelligence?

### Conclusion validity

• Statistical

• Appropriate statistics?

• Internal

• Really the cause?

• Construct (Measure)

• Measure what it is supposed to measure?

• External

• Will it generalize? (e.g., sampling)

### Statistical Validity

• Run any inferential statistics?

• Run appropriate inferential statistics?

• Assumptions of tests are met?

• Normality

• Homogeneity of variance

• Independence of variance

### Threats to internal validity

• Participant variables

• History (different past experiences)

• Maturation (more past experiences)

• Self-selection differences

• Mortality (some participants disappear)

• Selection process artifacts

• Testing (determining group changes them)

• Statistical regression (just different by chance the first time)

### Construct (measure) validity

• Face

• Sounds plausible on the face of it?

• Content

• Content details seem appropriate?

• Predictive

• Predicts things that it should predict?

• Concurrent

• Correlated with things that should be related? (but not too highly!)

### External validity

• Experiment versus real life:

• Participants