An article in the New York Times describes recent research by economists Brian Knight and Nathan Schiff on the relative impact of votes from different states in the presidential primaries. They estimate that a vote in an Iowa or New Hampshire primary has the impact of five Super Tuesday voters. The focus of the Times article is on the policy implications of this impact inequality. One of the interesting things about this research is how "impact" is measured. What the article doesn't mention is why there is any impact difference in the first place. After all, mathematically, a vote in Iowa or New Hampshire counts just as much as one in New Jersey or Montana.
The way the Knight and Schiff estimated "impact" was to look at election polls before and after each primary. They found that the polls shifted the most after early primaries. Their theory is that voters are uncertain about the quality of different candidates, but learn (or infer) something about that quality by observing others. This is kind of like noticing that a lot of people drive a certain type of car and then inferring that therefore it must be a pretty good car. But, we could imagine several other stories. For example, If voters that prefer candidate A perceive candidate B as a lock-in to win the nomination, then maybe they decide not to vote. Prospective voters for candidate B on the other hand may continue to vote because they enjoy being on the winning side. Some undecided voters may shift towards candidate B for the same reason. A question that has perplexed political scientists and economists for decades is why does anyone vote in the first place. A more careful look at these results could shed light on that question.