# Observational study

> ## RCT를 할 수 없는 이유들[^1]

## <RCT>를 할 수 없는 이유들[^1]

- Ethical reasons (e.g., unethical to randomize people to smoke for measuring effect on lung cancer)
- Infeasibility (e.g., can't randomize countries into communist/capitalist systems to measure effect on GDP)
- Impossibility (e.g., can't change a living person's <DNA> at birth for measuring effect on breast cancer)

## Footnotes

[^1]: [A brief introduction to casual inference](https://youtu.be/DXBPtpBhGqo?si=dApLXl8GN4NwEhFb&t=1935)