For decades, scholars have estimated the ideology of members of Congress by analyzing roll-call votes, recorded tallies of each member’s “yea-or-nay” on legislation.
But a new study from the University of Chicago's Harris School of Public Policy finds this method is likely skewed by "protest voting"—suggesting that polarization in Congress may be even greater, and started even earlier, than researchers thought.
“We often assume that votes in Congress directly reveal ideology,” said UChicago Prof. Anthony Fowler, first author of the study. “But sometimes legislators vote ‘no’ as a way of signaling dissatisfaction or sending a different message. Our goal was to account for those moments so we can better measure what legislators actually believe.”
To do that, Fowler, the Sydney A. Stein, Jr. Professor at Harris, and his coauthor Prof. Jeffrey B. Lewis from UCLA examined roll-call votes in the United States House from 1889 to 2022. In a paper published in the journal Political Analysis, they developed a new statistical model that allows for the possibility of protest voting—something previous approaches did not. They then used it to estimate ideological positions of House members over more than a century.
Protest votes, as Fowler and Lewis define them, come from members of the majority party voting against legislation they would otherwise support. They're rare—roughly 1% to 3% of votes—but the authors found that accounting for even that small share can significantly reshape how individual lawmakers appear on the ideological spectrum.
One striking example involves U.S. Rep. Alexandria Ocasio-Cortez, D-N.Y., and other progressive lawmakers sometimes referred to as “the Squad.”
Traditional roll-call models identify them as relatively moderate Democrats, between the 56th and 187th most liberal members of the House. This result appears inconsistent with their public rhetoric and policy positions. When the researchers account for protest voting, however, these lawmakers emerge as six of the seven most liberal members of Congress—much closer to what observers would expect. This likely reflects voting against policies they believe do not go far enough.
The adjusted measures also line up more closely with other indicators of ideology that do not rely on roll-call votes.
When Fowler and Lewis account for protest voting, they find that ideological polarization in Congress is even greater than previous estimates suggested. Their results also indicate that polarization began rising earlier than many scholars previously thought, well before the period often described as the “textbook Congress” from about the 1940s to the 1970s.
At the same time, the research highlights an important distinction—polarization does not necessarily mean strong party discipline. Highly ideological lawmakers, especially in recent decades, may be more likely to cast protest votes against their own party’s proposals. This means Congress can appear somewhat less polarized in traditional voting models even when ideological differences between parties are quite large.
Using their adjusted measures of ideology, Fowler and Lewis also find that voters appear to impose a stronger electoral penalty on ideological excess than previously estimated, which relates to Fowler’s larger body of work on the power of moderates and the median voter in electoral politics. The study finds no evidence that protest voting itself is rewarded at the ballot box.
In fact, all else being equal, members who engage in more protest voting tend to raise less campaign money, the paper finds.
Although protest voting rarely determines the outcome of a bill, the authors show that even a small number of these votes can influence how scholars interpret congressional behavior. Their findings suggest that researchers studying ideology, elections and representation may benefit from accounting for protest voting when analyzing legislative data.
“Roll-call votes remain an incredibly valuable source of information about congressional behavior,” Fowler said. “But our findings show that accounting for a small number of non-ideological votes can give us a clearer picture of where legislators actually stand.”
—Adapted from an article originally published on the UChicago Harris website.
