## 3.12 Unit 3 summary

### 3.12.1 You should be able to

• Conduct a statistical hypothesis test of an observed difference between two groups
• Write an appropriate null hypothesis for a study that compares two groups
• Use Monte Carlo simulation in TinkerPlots™ to find the expected variation if the null hypothesis were true (randomization test)
• Formulate a conclusion
• Evaluate the internal validity of a study using the following criteria:
• Temporal precedence
• Correlation of cause and effect
• No plausible alternative explanations

### 3.12.2 You should understand

• How to interpret the mean of a dummy variable
• How to interpret the difference in means between two groups
• The logic behind a randomization test, including:
• Why we take the observed outcomes as fixed
• Why we randomly reassign the observed outcomes to experimental groups
• Why we sample without replacement
• What the distribution of results represents
• What internal validity means
• The role of random assignment in drawing cause-and-effect conclusions (internal validity)

### 3.12.3 TinkerPlots™ skills

• Create a split dot plot
• Create a “shuffler” sampler
• Use the Ruler tool to find the difference in means

### 3.12.4 Vocab

• Categorical variable
• Numeric variable
• Dummy variable/Dummy coding
• Experiment
• Random assignment
• Observational study
• Confounding variable
• Internal validity/cause-and-effect
• Probabilistically equivalent