Regression Discontinuity Design (RDD) Skill

This skill covers sharp and fuzzy RDD: identification assumptions, bandwidth selection, local polynomial estimation, validity tests, and reporting standards for academic papers.

Core Logic

RDD exploits a known threshold in a continuous "running variable" (X) that determines treatment assignment. Units just above and below the cutoff (c) are comparable on all dimensions except treatment.

Sharp RDD: Treatment perfectly determined by crossing cutoff

• T_i = 1 if X_i ≥ c, T_i = 0 if X_i < c
• Estimand: Average treatment effect at the cutoff (τ_SRD)

Fuzzy RDD: Crossing cutoff increases probability of treatment (like an instrument)

• Use when there's non-compliance around the cutoff
• Estimand: LATE at the cutoff (τ_FRD = reduced form / first stage)

RDD Assumptions