Bad weather can change the course of political history. According to one account, a particularly nasty storm in 1960 kept rural, primarily Republican voters home on Election Day, tipping the balance in favor of John F. Kennedy. News reports disagree on which political party benefits most from bad weather, but they all agree on the cause: Inclement conditions keep people home.

But weather affects more than our ability to make it to the polls. In a recent paper, University of North Carolina political scientist Anna Bassi argues that depressing weather leads to bad moods, and those bad moods lead us to prefer safer, more predictable candidates — namely, incumbents.

To test that hypothesis, Bassi had 166 participants choose between two hypothetical candidates, whom she dubbed Mr. C, for challenger, and Mr. I, for incumbent. Selecting Mr. C was risky: There was an equal chance of earning either $8.40 or $13.20 (independent of the experimental condition), and which one a subject got would be determined only after he or she had chosen the challenger. Meanwhile, Mr. I was a safe bet: While the actual amount earned varied across experimental conditions, participants always knew beforehand what choosing the incumbent would net them.

Where does weather come in? Before approaching potential subjects, Bassi chose dates for the experimental sessions based on the forecast — one set of sunny days, and one set of cloudy ones. To ensure that she tested for the effects of actual weather rather than forecasts, she constructed two indicators of good weather: whether the day was predominantly sunny and whether rainfall that day was less than the local daily average of about 0.12 inches. Finally Bassi gauged each participant's subjective assessment of the weather using a seven point scale, ranging from "Terrible" to "Awesome."

In most cases, bad weather yielded the incumbent, Mr. I, a 10 to 20 percent boost, depending on which of the metrics Bassi used to define good and bad weather. Those results held up, Bassi found, when controlling for other factors such as race, gender, and political leanings. A detailed follow-up survey suggested that much of the weather-based difference in choice could be accounted for by mood — when bad weather made for more negative moods, that led participants to choose the safe incumbent more often.

Those results are at odds with media reports, which generally argue that bad weather suppresses turnout, in turn, favoring one party or the other, Bassi writes. While there's no consensus among researchers about the overall effect of inclement weather on an election, her experiment suggests that a storm or heavy rain really could change the political landscape — and in different ways than anyone had previously thought.

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