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We compared the Supreme Court with other democracies’ high courts. More justices would improve its work.

More justices could produce more opinions — and improve consistency in U.S. law.

Recently President Biden established a commission to consider altering the Supreme Court, marking the first time the United States has seriously discussed expanding the court since President Franklin D. Roosevelt’s attempt in 1937. Roosevelt argued adding up to six justices would increase the court’s productivity. But many recognized this as a thinly veiled justification for appointing liberal justices who would affirm New Deal policies.

Research demonstrates the court had no crisis of productivity in 1937. In fact, the Depression-era court heard nearly 20 percent of the cases appealed to it and issued more than twice the written opinions it does today.

The current court is far less productive. Our analysis of historical and comparative data finds increasing the number of justices on the court would increase its productivity and contribute to greater consistency in U.S. law.

The Supreme Court’s productivity has dropped significantly

Today’s court writes opinions in remarkably few cases, when compared with its past. From 1933 to 1937, during the New Deal, the court annually received 835 appeals and wrote opinions in 164 of them. From 2015 to 2019, by contrast, the court annually received 7,276 appeals and averaged 68 opinions per year. Thus, the country’s highest court now writes opinions in only 1 percent of appeals, as compared to 20 percent during the 1930s, leaving important legal questions unanswered.

What is the Supreme Court’s job?

Two of the court’s fundamental tasks are resolving disagreements among lower courts over the meaning of federal law and correcting errors made by lower courts in interpreting and applying law.

When two or more of the 12 U.S. courts of appeals issue rulings that disagree, it’s called a “circuit split.” This means the regions those courts cover — say, the West Coast under the Ninth Circuit and Texas under the Fifth, to name two appeals courts that commonly disagree — interpret federal law differently. Only the Supreme Court can resolve these disagreements. From 2014 to 2017, litigants asked the court to resolve 66 circuit splits each year. Because it takes few cases, the court does not resolve all significant splits. Political scientists show two-thirds of circuit-split appeals go unresolved for long periods, possibly forever — meaning, say, the citizens of California (Ninth Circuit) and Texas (Fifth Circuit) live under different laws.

The Supreme Court is also responsible for correcting inaccurate lower court decisions. The court’s current productivity implies lower court decisions are incorrect in only 1 percent of appealed cases.

Biden’s court reform commission is examining term limits. Those could have unintended consequences.

How does the U.S. Supreme Court compare with other nations’ high court?

Will adding justices increase the court’s output? We examined other nations’ top courts and found that spreading the workload among more judges lets a court decide more cases.

In the figure below, we averaged the annual number of decisions between 2015 and 2019 issued by 24 supreme and constitutional courts against the number of judges in each court.

Courts with more judges decide more cases. A larger number of judges supports a greater division of labor for managing procedure and writing opinions. Adding about three judges to a court increases its productivity by almost 92 opinions per year. That relationship exists because courts spread the workload across its members.

For instance, the Supreme Court follows a norm of equity, assigning each justice about the same number of majority opinions each term. In addition, the majority opinion author is responsible for writing the majority opinion and thus spends far greater time working on it than most other justices. The opinion-writing process requires that justice to pen the first draft and circulate subsequent drafts, as necessary, to address concerns raised by other justices and thereby encourage them to join it. Research shows the majority opinion author circulates about three draft opinions before finishing work on the majority opinion after almost 80 days.

If the court had additional justices and each of the new justices wrote their share of majority opinions, the court could decide more cases. To be sure, research shows justices bargain and negotiate during the opinion-writing process based on ideological and strategic concerns. Despite this, we don’t expect expanding the court to substantially lengthen the time it takes to write opinions or undermine the effect additional justices would have on productivity.

More specifically, based on the comparative data, if the court had between 12 to 26 justices, it could write opinions in, respectively, about 150 to 300 cases annually. Basing this calculation only on the U.S. Supreme Court’s recent production of opinions then adding 12 to 26 justices would increase the annual number of opinions to, respectively, 96 and 208.

By deciding more cases, the court can resolve more circuit splits and correct more lower court errors, reducing inconsistency in U.S. law and offering greater guidance on thorny legal questions.

Notice that one of these courts is similar in size to the U.S. Supreme Court but produces markedly more decisions: the French Constitutional Council. It must rule on all appeals (unlike the U.S. court, which can choose which cases to decide) and meet a strict, short deadline. Not surprisingly, each case receives a terse ruling. The Supreme Court’s opinions, by contrast, are long and analytically complex — averaging more than 5,000 words per majority opinion — and including separate opinions in over 80 percent of cases. This comparison is instructive, highlighting the price of greater productivity with only nine justices. If the court moved to a system like the French Constitutional Council, it might undermine its ability to effectively communicate its decisions.

There would probably be more yawns than outrage if Biden expanded the Supreme Court

The politics of court changes

Expanding the court isn’t straightforward, given the extreme partisan polarization in Congress and the public. But since more justices might make the court as productive as other nations’ high courts, politicians have a nonpartisan reason to cooperate on changes. Expansion could include regulations to prevent one political party from stacking the court, reducing the stakes for each individual appointment. This could reduce the pressure to play “constitutional hardball” with any single vacancy. With more written opinions, U.S. law could be more consistent and clear.

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Clifford J. Carrubba is the Samuel Candler Dobbs professor in political science and chair of the department of quantitative theory and methods at Emory University, and author of “International Courts and the Performance of International Agreements” (Cambridge University Press, 2014).

Matthew J. Gabel is professor of political science, affiliated faculty of the center on empirical research in the law; research fellow of the Weidenbaum Center on economy, government, and public policy at Washington University in St. Louis; and author of “International Courts and the Performance of International Agreements” (Cambridge University Press, 2014).

Jay N. Krehbiel is assistant professor of political science at West Virginia University.

Sivaram Cheruvu is a PhD candidate in political science at Emory University. He begins as an assistant professor of political science at the University of Texas at Dallas in fall.

James F. Spriggs II is the Sidney W. Souers professor of government and affiliated faculty of the Center for Empirical Research in the Law at Washington University in St. Louis. He is author of “Crafting Law on the Supreme Court” (Cambridge University Press, 2000) and “The Politics of Precedent” (Princeton University Press, 2006).