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Momentum and Legitimacy in Presidential Primaries

- April 22, 2008

Brian Knight and Nathan Shiff have an “interesting new NBER paper”:http://weber.ucsd.edu/~jlbroz/PElunch/knight_schiff_momentum.pdf on momentum and voter choice.

This paper provides an investigation of the role of momentum and social learning in sequential voting systems. In the econometric model, voters are uncertain over candidate quality, and voters in late states attempt to infer the information held by those in early states from voting returns. Candidates experience momentum effects when their performance in early states exceeds expectations. The empirical application focuses on the responses of daily polling data to the release of voting returns in the 2004 presidential primary. We find that Kerry benefited from surprising wins in early states and took votes away from Dean, who held a strong lead prior to the beginning of the primary season. The voting weights implied by the estimated model demonstrate that early voters have up to 20 times the influence of late voters in the selection of candidates, demonstrating a significant departure from the ideal of “one person, one vote.” We then address several alternative, non-learning explanations for our results. Finally, we run simulations under different electoral structures and find that a simultaneous election would have been more competitive due to the absence of herding and that alternative sequential structures would have yielded different outcomes.

This brings the US primary system, which I’d never really thought about in this way before, under the rubric of things that I find deeply weird as a foreigner about the US political system. I won’t pretend to comment on the modeling strategies or econometrics in the Knight and Shiff piece – but if the estimate that they provide (or even the estimate under an alternative specification that Iowa voters were six times as influential as Super Tuesday voters) is at all ballpark, isn’t there something problematic about a system in which the disparities in influence are as gross as this? And yes: the same point _does_ apply to Senate voting too – but that’s impossible to change without changing the constitution, while a simultaneous election would only require calling Iowa’s and New Hampshire’s bluff (this is one situation where the one-shot game prediction that all states would converge on the earliest possible date would be superior to the current arrangement).