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Regression-Discontinuity Design - Institute for Policy Research

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Nonlinearities in Functional Form<br />

• Anything that affects the size of that discontinuity<br />

other than treatment is a threat.<br />

• In the example, we assumed the relationship<br />

between assignment and outcome was linear—<br />

regressions are straight lines.<br />

• But functional <strong>for</strong>m can be nonlinear due to:<br />

– Nonlinear Relationships between the assignment<br />

variable and the outcome<br />

– Interactions between the assignment variable and<br />

treatment.

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