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Regression Discontinuity - Institute for Policy Research

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Power Considerations Unique to RD: Variance of<br />

Impact Estimator in RDD<br />

Var rd (α^<br />

1 ) = σ 2 (1-R rd2 )<br />

np(1-p)(1-ns-co) 2 (1-R ts2 )<br />

• All other terms are the same, except:<br />

• R ts<br />

2<br />

is the square of the correlation between<br />

treatment status and assignment variable – higher<br />

the value less power (and more co-linearity)

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