Your vote is precious, almost sacred. It is the most powerful nonviolent tool we have to create a more perfect union. - John Lewis, Civil Rights Leader & Former U.S. Congressman
Elections and Diversity
This post was written during the height of election season in 2024, when the people across each of the United States choose representatives to govern them. When it comes to democratic elections, the spotlight usually lands on the presidential race. But, the real story might be hiding in plain sight down the ballot. By looking at performance in past local elections, we can glean valuable insights into how future races can be better supported by parties - meaning that people get more options for representation. This insight is valuable to those considering running for office and anyone who supports democracy.
A "down-ballot" race refers to local and state races on an election ballot, like those for governors, state legislators, and city councils, positioned below the high-profile races such as presidential or congressional elections. They often occur more frequently than high profile races, as well as having more offices to fill and more candidates. Down-ballot races often have more options, but does that mean people vote differently than the general election? This brings up the concept of diversity, a tool used in social science, as a lens for understanding elections. We say the way things are spread out (or distributed) is diverse if it has close to an equal share. Things lack diversity when the share is more concentrated. You might be wondering: How can diversity in local elections tell us anything about the next presidential race? Think of voting as similar to making choices in a group project. The more people with different views, the more options on the table. If everyone thinks alike, decisions are simple, but where views vary widely, decisions require compromise, forming alliances, and finding middle ground.
In this post, we review this idea of voting diversity using the Green Mountain State of Vermont to illustrate the idea, then discusses why diversity matters.
The HHI
One powerful tool to understand diversity is something called the Herfindahl-Hirschman Index (HHI), related to something known as the "Effective Number of Parties" from political science. The idea of this index is to help us see how diverse voter preferences are in different regions and predict how those preferences might play out in the big races
In elections, this diversity shows up in the HHI, which measures how much a voting base "sticks together" or leans towards multiple options. A low HHI means people are spread out in their choices—say, voting for different parties or candidates. A high HHI means they’re concentrated around one or two options. By studying this spread, especially in local elections, we can get a sense of how strong or fragile any one candidate's or party's appeal is.
Using the HHI, we look at down-ballot races from Vermont using data from Harvard's Dataverse. The image below shows the diversity of the 2020 Presidential election results. (Some areas have no available results in the source data due to low population, including the locales of Warren's gore, Avery's gore, Lewis town, or Somerset town).
The areas in deep purple show a lack of diversity, but most of the area in the state shows an HHI of 0.5 or lower, which means the effective number of candidates in a race is two or more.
On seeing that, you might think that Vermont prefers one party over another. Surprisingly to those who don't live there, including me, Vermont votes for a diverse range of parties generally, such as a GOP Governor in 2020.
This diversity is seen in the difference in the HHI between the presidential and more local races like state attorney general, governor, etc. The next image shows that difference. In the area of Burlington, HHI is much larger in the Presidential race (by 15%) compared to the average local race. But in many areas of the state, local races are significantly less diverse than the Presidential race, meaning local races tended to be more concentrated.
We can see what this looks like if we plot the Presidential 2020 HHI and its difference to the local races (or, the concentration margin for the Presidential election). There is a clear positive trend between the two, which means that when the presidential race is more concentrated, down-ballot races statistically perform with lower concentration overall.
This result is consistent when we compare down-ballot races of 2018 to the 2020 presidential election.
This difference in diversity between the local and Presidential races could be interpreted in a number of ways, two in particular being useful for anyone building an election strategy: (1) high enthusiasm for the top level race; (2) willingness to vote for other parties on down-ballot.
How diversity impacts election strategy
One may think that 2018 and 2020 are special cases for a variety of reasons. Regardless, the similarity in the performance of down-ballot races between years should not be ignored. If we think this relationship over time holds in 2024, 2026, and beyond, then the HHI can be used to shortlist areas where political strategists work to strength the performance in down-ballot races, potentially winning or strengthening their lead in an area.
Conclusion
In a democracy, diversity in voter preferences enriches representation, giving voice to a wider range of viewpoints. By examining down-ballot races and applying tools like the HHI, we can better understand how concentrated or spread out voter support truly is. This knowledge can guide strategies for future elections, helping political parties and candidates address the real preferences of communities across the nation. In short, measuring and fostering diversity in local races isn't just about statistics—it's about ensuring that democracy remains vibrant and inclusive, where every vote shapes a more representative future.
By Tom Roderick, PhD from Flamelit
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