Joshua Tucker: The following is a guest post from New York University-Abu Dhabi political scientist Adam Ramey.


When scholars and pundits talk about Congress, ideology is one of the most frequently cited terms. All of the talk of partisan polarization, gridlock, and the seemingly impossible task of reaching compromise is almost always framed using this concept. We all know the basic story: in the last few decades, Democrats have become more liberal and Republicans have become more conservative. As the political center has evaporated, so too has the collegiality and spirit of bipartisanship.

As the parties have become more cohesive, ideology has become one of the best predictors of how legislators vote. Political scientists Keith Poole and Howard Rosenthal have documented this in their vast body of research, showing the increasing prevalence of a single left-right ideological divide in congressional voting behavior. Countless scholars have used their measures of legislator ideology to predict a whole host of behavior on-and-off the floor.

While there is no denying that ideology explains a lot, it cannot explain everything on its own. For example, in the last few years, we have seen increasing disagreement within the Republican caucus over tactics. While most members of the Republican caucus are ideologically conservative, they pursue their goals in different ways. Some think the best way to pursue to policy goals is to forge compromise. Others think the best tactic is to defund the federal government, taking the floor of Congress and Twittersphere by storm to advance their agenda. Indeed, ideology (alone) cannot explain this variation in behavior that we are currently witnessing. That begs the question: if not ideology, then what exactly?

In a new paper, my colleagues (Jonathan Klingler and Gary Hollibaugh) and I argue that personality and ideology work together to shape how legislators make decisions, voting and otherwise. Using every floor speech by every member of the U.S. Congress since 1996, we use some recent methods in computer science to generate the first estimates of legislator personality over time. For each member, we estimate their positions on the Big Five personality dimensions – Openness to new experiences, Conscientiousness, Extraversion, Agreeableness, and Neuroticism (or OCEAN, for short). We find that each of these dimensions helps us to explain lots of different behaviors that legislators engage in, even after accounting for ideology.

Intriguingly, it turns out that personality traits help us to tell a nuanced story of what is going on in Washington. Specifically, it’s not just liberals behaving differently than conservatives. Rather, most of the dysfunction we observe in Congress today is a product of both ideology and changing personality demographics.

To make this point clear, let’s look at two simple examples: co-sponsoring a bill with members of a different party and missing votes. For cosponsorship, we argues that, irrespective of ideology and electoral concerns, Agreeableness–“the tendency to act in a cooperative, unselfish manner”–should explain why some legislators are more likely to cosponsor with members across party lines. Figure 1 (below) shows the results of our statistical model predicting bipartisan cosponsorship as a function of Agreeableness from 1996-2009. The different lines are separated based on whether the legislator was from a safe, marginal, or razor-thin (50/50) district. Predictably, people from closer districts engage in bipartisan cosponsorship more often than those from safe ones. However, across all three categories, more agreeable legislators cosponsor across the aisle a lot. Visually, we see varying agreeableness from the lowest to highest values is worth an extra 20 cosponsored bills on average (a 10-point increase in the rate of bipartisan cosponsorship)!

In the case of playing missing votes, we argue that, again controlling for ideology, increased Conscientiousness–“the tendency to be organized, responsible, and hardworking”–should make legislators less likely to miss votes on the floor. Sure, some legislators miss votes for personal reasons – health, family, district issues, etc. However, in the aggregate, the more conscientious folks should miss fewer votes. Sure enough, our statistical analysis of absenteeism from 1996-2012 confirms this. Figure 2 shows the number of absences predicted for varying levels of Conscientiousness. Going from the least to the most conscientious legislator values, the number of absences decreases from about 75 to around 30 (lowering the absentee rate overall from 6 percent of votes to less than 3 percent).

This is only the tip of the iceberg. Our findings show that personality dimensions explain the kinds of bills legislators propose, how often they buck the party line, how they use press releases and Twitter to disseminate information, and more. All together, this leads to a simple but profound conclusion: personality is more than a feeling. It’s a driving force behind partisan, polarizing tactics and it’s reshaping how Washington works.