GV249 Seminar WT10: Mechanisms

📋 Outline

• Why study mechanisms?
• Strategies for studying mechanisms
• Exercise

🍋 Why study mechanisms

🍋 Why study mechanisms

Limes and Scurvy

• In the 1700s, British Navy sailors were suffering from scurvy. No one knew how to treat it.
• James Lind conducted an RCT and found that sufferers of scurvy responded well to eating citrus fruit.

🍋 Why study mechanisms

🍋 Why study mechanisms

• Fresh limes are hard to store, so the Navy boiled lime juice to preserve it.
• Limes stopped working at curing scurvy. Why?

🍋 Why study mechanisms

🔎 Strategies for studying mechanisms

Causal mediation analysis

• In sum: measuring mediators and then controlling for them to see if they explain the relationship between treatment and outcome.
• Problematic: when \(M\) is not randomly assigned, it can be confounded by unobserved mediators.

🔎 Strategies for studying mechanisms

Implicit mediation analysis

• Theorize what might mediate the relationship and think of “observable implications.”
• Test these implications in your analysis.
  • In an experiment, add additional treatment arms that either include the mediator or not.
  • In a quasi-experiment, look for any evidence you can use to support or reject observable implications.

🔎 Strategies for studying mechanisms

• Qualitative methods
  • Theorize what might mediate the relationship and explore these factors in interviews, focus groups, or records.
  • Often used to supplement quasi-experiments where implicit mediation analysis is more difficult (because the researcher cannot “add” treatments).

🏃‍♀️ Exercise