President-elect Donald Trump and House Speaker Paul D. Ryan (R-Wis.) on Nov. 10. (Alex Brandon/AP)

Many key questions will confront the new Congress when it begins its session this week. Will Republicans hold together to advance the agenda items they share with the incoming president, Donald Trump? And if the GOP splinters, as it did in the last session, could a broader coalition of some Republicans and some Democrats come together to pass legislation? And will Democratic leaders be willing to seek such compromises, or will they reject outright all Republican and Trump proposals?

These are just versions of perennial questions that confront members of Congress, who can pursue partisan or bipartisan strategies to achieve their legislative goals. But which is more effective? Our research finds that bipartisan legislators tend to be more effective. Moreover, bipartisanship helps even the strongly ideological members you’d least expect to work across party lines.

What we did

Our new research is part of our Legislative Effectiveness Project. We have developed a unique Legislative Effectiveness Score for members of the House of Representatives. These scores combine 15 indicators of lawmakers’ success at moving their bills through the legislative process.

We then wanted to see whether legislative effectiveness depended on how bipartisan a legislator was. To measure bipartisanship, we rely on the Bipartisan Index developed by the Lugar Center. This index captures the extent to which members of the other party co-sponsor a lawmaker’s bills and the extent to which that lawmaker co-sponsors bills of the other party.

What we found

Bipartisan lawmakers are indeed more effective. A typical lawmaker with above-average bipartisanship is about 11 percent more effective than a typical member with below-average bipartisanship. This means that a bipartisan lawmaker will push a larger legislative portfolio further through the lawmaking process. This is true even after accounting for other factors that also impact effectiveness, such as whether a member is in the majority party, head of a committee or subcommittee, or more senior.

But bipartisanship is particularly helpful for certain kinds of members. First, and unsurprisingly, it matters even more for minority-party members, who cannot move their bills forward without majority-party support.

Second, women in Congress tend to be more bipartisan, and that seems to help them be more effective. Surprisingly, bipartisanship helps women even when they are in the majority. Perhaps women are more likely to recognize that neither party has a monopoly on solutions for the policy problems they care about.

For example, consider Rep. Ileana Ros-Lehtinen (R-Fla.). Her United States-Israel Strategic Partnership Act of 2014 earned 355 co-sponsors and was praised upon its passage for its bipartisanship. Given the split on Israel between President Obama and Trump, congressional bridge-building on this issue may be quite valuable.

Third, the effect of bipartisanship depends on ideology. Centrists are typically more bipartisan than more strongly ideological lawmakers, but bipartisanship still pays off for the latter, even if they have to make a concerted effort to find common ground with the opposite party.

As one example, Rep. Edward R. Royce (R-Calif.) has been consistently conservative across his career in Congress. Throughout the 1990s and the early 2000s, he did not score high in either bipartisanship or effectiveness, in line with what our statistical models would predict. More recently, however, and especially after assuming subcommittee and committee chair positions, he has advanced more bipartisan legislation, such as the Credit Union Share Insurance Fund Parity Act and North Korea Sanctions and Policy Enhancement Act of 2016. Royce now scores as more effective than would be expected given his seniority and chair positions.

Finally, we have found that bipartisanship is actually a more effective strategy now than in the past. This is perhaps surprising, given that Congress is increasingly polarized. Of course, polarization means that legislators are less bipartisan now than previously, which means that bipartisanship takes more effort. But for those interested in advancing legislation to address America’s pressing problems, bipartisanship offers a good return on that investment.

Craig Volden is professor of public policy and politics at the Frank Batten School of Leadership and Public Policy at the University of Virginia. Alan E. Wiseman is a professor of political science and law at Vanderbilt University.