What's in a score?
Today’s post is about a data source that admittedly isn’t my favorite, but it’s a resource that’s commonly used (and thus, important to understand!): DW-Nominate Scores.
If you’re like whaaat are those, you are not alone. DW-Nominate scores are a political science measure of ideology (how conservative or liberal someone is). But if you’ve read headlines like, “Vice President Kamala Harris was ranked the most liberal Senator,” then you’ve likely already read about DW-Nominate scores.
But there is a caveat to this data. DW-Nominate scores use a rather blunt measure to capture ideology: congressional votes. This worked for the majority of congressional history, when there were more votes on the floor and the two parties were not clearly divided along ideological lines.
But today, parties are very unified. So instead, DW-Nomiante scores more accurately capture party loyalty—how often members vote with their party. So as a Senator, VP Harris may not have been that “liberal”, but rather, a really loyal Democratic member.
But a caveat to the caveat: DW-Nominate scores are still widely accepted as the standard for ideology. For one, there are few other options for accessible, replicable data other than votes. Plus, they aren’t totally useless. As we’ll see in the examples below, they do capture some degree of ideology.
This post is going to give you an overview of DW-Nominate Scores, how they’re calculated, how to find and download them, and how to interpret them.
Using DW-Nominate Scores
So, what are DW-Nominate Scores?
DW-Nominate scores were created by political scientists Keith T. Poole and Howard Rosenthal in the 1980s. They created a formula that scales individual votes of legislators with every vote during the congressional session.
The result is a “map” that illustrates where members of the chamber fall ideologically. Every member is given a score from 1 (most conservative) to -1 (most liberal). Below is an example from the 117th House of Representatives:
Some votes are “weighted” more, resulting in two dimensions of DW-Nominate scores. The first dimension captures the most salient issues of the congressional session—think the “hot button” issues like the economy, social issues, etc. The second dimension is more procedural, and less commonly used. We will only discuss the (more relevant) first dimension.
How to find and use DW-Nominate scores:
DW-Nominate scores are super accessible and easy to download via VoteView.com. This website is awesome! Here, you can look up individual legislators and votes, download entire spreadsheets of information, and even find historical congresses. As shown below, the home page shows revolving examples of “key votes” in history.
But let’s get into the data! First, we’ll start by looking at how members of Congress compare with their peers. Go to the homepage and click “chamber” at the top of the screen. Select House of Representatives or Senate.
I’ll use the 117th Senate as an example. On the top left of the screen you can change it to any congressional session you’d like (all the way back to the very first Congress!).
Each of the blue and red dots in the oval below represents a Senator or Representative. If you click on the dot, you can see the name and biographical information of the Senator. The blue dot right in the middle? Senator Joe Manchin (D-WV). The red dot in the lower center? Senator Susan Collins (R-ME).
You can also search for members directly by name (bottom right), or on the home page.
Another very cool feature is seeing how your district has changed over time. Head back to the homepage and click the geography tab. Type in your address or zip code to see the current and former members that represented you—including the very first year your area was included in Congress (remember, Congress hasn’t always been 435 seats or 100 senators! States were added until the 50s, and congressional seats are added and removed every ten years).
The party tab will show you how political parties have evolved overtime, as well as the ideology of now-defunct groups like the Whig Party. Obviously, there is a ton to explore on this website, for current-day hacks and historical nerds alike.
How to download the data directly:
For those who want a hand spreadsheet of votes and biographical information, head to the data tab.
Here, you can build your spreadsheet using the drop-down options. In addition to ideology, you could also download every member vote, or just the parties’ information. The spreadsheet for ideology also includes biographical information like name, DOB, and district information (very handy!).
After you select the options you’d like, just download as a CSV file to your computer, and voila! The data is ready to go.
Pros and Cons of DW-Nominate
Pros: Obviously, it’s super accessible and easy to update on a regular basis. Votes are much easier to capture than things like financial expenditures or interest group support. Votes are also reflective of, well, actual representing, and are easy to communicate and understand.
Plus, it is clearly capturing some degree of ideology. The fact that Senators Manchin and Collins are in the center of the graph, and Senators Elizabeth Warren (D-MA) and Mike Lee (R-UT) are on the fringes of their respective party reflects what we know to be true about their ideological leaning.
But… Cons: DW-Nominate scores are based on votes. For the majority of history, there were a lot of votes, and a lot of cross-party voting. Single-issue bills were common, and being a Democratic member of Congress didn’t mean you had liberal ideals, nor did being a Republican make you conservative.
But after the southern realignment in which southern Democratic members were swapped out for Republicans (and northern cities became Democratic strongholds), the parties centralized, becoming more unified and relying more on congressional leaders to build large, legislative packages that could win majority support.
Today, votes are more reflective of party loyalty than ideology. Senator Collins has voted with the Democratic Party more than her colleagues—that’s why she’s in the middle, not necessarily because she’s a moderate. Further, when you look at folks like Senators Bernie Sanders (D-VT) or Tom Cotton (R-AK), who are certainly “fringe” members, they’re located right in the middle of their party’s pack. This is because they vote with their party more often than those who abstain or vote against bipartisan provisions.
TL;DR, DW-Nominate is informative, but today it’s more reflective of party unity than ideology. That being said, VoteView is still an awesome tool, DW-Nominate is still the easiest way to measure ideology, and there’s a lot of explorin’ you can do.
As always, send any questions/ comments/ suggestions my way!