A new document has been added to the Society for Political Methodology Website.

Title:   How Much is Minnesota Like Wisconsin? States as Counterfactuals

URL: http://polmeth.wustl.edu/mediaDetail.php?docId=1188

Author(s):  Luke Keele and, William Minozzi

Entry Date:     07-10-2010

Keyword(s):   causal inference, voter turnout, placebo tests, research 
design


Abstract:

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.

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