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We explore the use of geographic boundaries as regression discontinuities, studying designs where the assignment variable is distance to a boundary and subjects on either side of this boundary are compared. We develop the identification assumptions behind RD designs of this type and suggest that the key assumption is more likely to be violated, since agents are better able to sort around the discontinuity. Moreover, we show that geographic RD designs that employ a naive notion of distance as the assignment variable fail to recover the treatment effects of interest. We develop an new estimator that is faithful to the inherently spatial qualities of the design and a method to test between identification strategies. We illustrate our argument and method with an application on whether ballot initiatives increase turnout. Specifically, we focus on a 2008 initiative to provide paid sick leave that was on the ballot in the city of Milwaukee but not the rest of the state. We find no evidence that turnout increased due to the ballot initiative. [ABSTRACT FROM AUTHOR]

Political scientists are often interested in understanding whether state laws alter individual level behavior. For example, states often alter their election procedures, which can increase or decrease the cost of voting. In this example, it is important to understand whether these changes alter turnout since changes in costs may disproportionally affect those at the margin of voting. Analysts have typically used one of two different regression based research designs to estimate whether changes in state laws increase or decrease turnout. In both instances, voters from states without a change in laws are used as counterfactuals for the voters who experience a change in election law. Here, we carefully examine the assumptions behind both research designs and study their plausibility. Next, we outline a series of research design elements that can be used in addition to the usual designs. These research design elements allow the analyst to better understand the role of unobserved confounders, which is obscured in standard research designs. Using these design elements, we demonstrate that what appears to be clear cut evidence from the usual research designs is often a function confounding. We argue that to truly understand how changes in voting costs alters turnout, a different research design is required. Future work must rely on a research design that makes comparisons among voters who live within the same state. Our work has implications beyond turnout to any investigation of how state level treatments alter individual behavior. [ABSTRACT FROM AUTHOR]