A new University of Massachusetts Amherst study finds that U.S. Supreme Court justices affiliated with the conservative legal organization the Federalist Society—including six current justices—are both more likely to vote conservatively and more consistent in doing so than their non-affiliated counterparts, a pattern that could shape American law for decades.

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The analysis, by Paul Collins, professor of legal studies and political science, and Tim Komatsu, doctoral student in political science, examined nearly 25,000 votes cast by Supreme Court justices between 1986 and 2022. They show that justices with ties to the Federalist Society were about 10 percentage points more likely to vote in a conservative direction compared to justices without such connections. The study, published in PLOS One, also concluded that affiliated justices rarely deviated from conservative ideological positions, creating a more unified and predictable bloc on the high court.

Komatsu explains, “Our research seeks to understand how interested parties are able to affect change within the Supreme Court—the branch of the government with the most institutional protections against influence. We found that the Federalist Society has been extremely successful in ensuring that the Supreme Court reflects its values.”

The Federalist Society, founded in 1982, has grown into one of the most influential organizations in the conservative legal movement. Its network spans law schools, government positions and the judiciary. The group does not litigate or formally endorse policies but serves as a hub for training, networking and advising, especially on judicial nominations. Republican presidents from George H.W. Bush to Donald Trump have relied heavily on the organization when selecting judicial nominees.

Every Republican-appointed justice currently on the court—Chief Justice John Roberts and Justices Clarence Thomas, Samuel Alito, Neil Gorsuch, Brett Kavanaugh and Amy Coney Barrett—is affiliated with the Federalist Society. Earlier Republican nominees such as Anthony Kennedy and David Souter were not connected to the group, and both at times sided with liberal justices in major rulings. The study suggests that the rise of Federalist Society-affiliated nominees has reduced the likelihood of similar ideological crossovers.

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Using statistical modeling, the researchers found that Federalist Society justices’ voting patterns remained consistently conservative even after controlling for broader measures of judicial ideology. In other words, affiliation itself was a stronger predictor of conservative consistency than ideology alone.

This consistency, Collins and Komatsu argue, has helped advance the goals of the conservative legal movement, which include originalist interpretations of the Constitution, limiting government regulation and overturning liberal precedents on issues such as abortion and gun rights.

The findings come at a time when the court’s recent decisions—including the overturning of Roe v. Wade, the expansion of gun rights and limitations on federal regulatory authority—have already transformed American law and politics. Critics of the court have raised concerns about its legitimacy, while supporters have hailed the rulings as a return to constitutional principles.

“Whether you agree or disagree with their conservative agenda, there is no doubt that the Federalist Society has a substantial influence on American law,” Collins notes. “And with six Federalist Society-affiliated justices on the current Supreme Court and hundreds more in lower federal and state courts, this agenda will be etched into law for decades to come.”