1- Estimated Rate: $\frac{1}{n} \sum_{i=1}^n Y_{i}$

• Target population: Mean over every i among U.S. adults
• Unit-specific quantity ($Y_{i}$): Whether each i is employed

2- Causal question: How would the probability of employment differ if we enrolled a randomly chosen individual in job training or not? $\frac{1}{n} \sum_{i=1}^n \left( Y_{i}(1) - Y_{i}(0) \right)$

• Target population: Mean over every i among U.S. adults
• Unit-specific quantity: Whether each i is employed
  • $Y_{i}(1)$: Employment if enrolled in job training
  • $Y_{i}(0)$: Employment if not enrolled in job training