Question 1

RDD or DID — which is better for my research?

Accepted Answer

RDD requires a clear cutoff value and subjects cannot precisely manipulate assignment. DID requires parallel trends. RDD suits research with hard policy thresholds; DID suits panel data with parallel trends.

Question 2

How to choose the bandwidth?

Accepted Answer

Use Imbens-Kalyanaraman optimal bandwidth (rdrobust default). Report multiple bandwidths (0.5x, 2x optimal) as robustness checks.

Question 3

How to estimate Fuzzy RDD?

Accepted Answer

Fuzzy RDD uses IV (2SLS) — use "crossing threshold" as instrument for "treatment status". Stata: `ivregress 2sls y (treat = crossing) x`.

Regression Discontinuity Design (RDD) Guide | Sharp RDD vs Fuzzy RDD, Bandwidth Selection and Stata Operations

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