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What influences the Supreme Court? Here’s what we learned.

The reasoning in amicus briefs shows up in the decisions. Lawyers’ experience makes a big difference as well.

The U.S. Supreme Court begins its new term Monday. (Joshua Roberts/Reuters)

The Supreme Court begins its 2022 term Monday, in the shadow of its momentous last term. In the final weeks, the court released important decisions that fundamentally changed constitutional law regarding gun rights, abortion and environmental protection, among other important issues. The upcoming term may grab just as many headlines. The justices will hear important cases about college admissions, states’ ability to regulate commerce and copyright law. Just in these first few days they will consider the standard under which the Environmental Protection Agency can regulate wetlands and the power of states to control elections in light of federal voting rights.

How do the justices make their decisions? Decades of research suggest that while their ideologies have an influence, that’s not the only influence. In our new book, we examine how information flows to the court and what the justices do with this information. Attorneys spend hours learning to craft arguments and clients spend large sums for such work. The parties in the lawsuits give the justices written arguments called “party briefs.” But other groups can weigh in, too. Interested groups and individuals can make written arguments in what are called “amicus curiae” or friend-of-the-court briefs.

These briefs matter, our research finds. They influence both who wins and how the justices write opinions that will shape future cases. But other resources, such as experienced attorneys, matter as well.

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How we know briefs influence the Supreme Court

To do our research, we use measures from relevant texts. For instance, borrowing from text analysis, we use a measure computational linguists call “cosine similarity scores” to see which briefs are most like the resulting opinions. This approach weights unusual words more than common terms, so that everyday language contributes less to the score than rarer or more specific words. For instance, in Justice Samuel A. Alito Jr.’s opinion in Dobbs v. Jackson Women’s Health Organization, the case in which the Supreme Court overturned Roe v. Wade, we found frequent use of the term “quickening” — which was often used in the Thomas More Society’s amicus brief.

We also consider novel language within briefs using something called “term frequency — inverse document frequency.” This accounts for how much of a brief is devoted to discussing concepts that scarcely show up in other briefs. Finally, we measure many things about the parties themselves, the organizations filing amicus briefs, and their attorneys — for instance, the attorneys’ years of experience — that can shape the results.

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These approaches can help us understand recent decisions

For instance, let’s apply these tools in examining Dobbs v. Jackson. As you can see in the figure below the two sides were equally matched on many factors that influence the outcome and the content of the opinion, like total number of words, types of information, and the novelty of the information.

We see that the side seeking to overturn Roe had a significant advantage in the experience levels of the attorneys listed first on the briefs. We also looked at the attorneys named on the 136 amicus briefs filed, many of whom are among an elite circle of specialized lawyers who regularly practice before the Supreme Court. Those seeking to overturn Roe collectively had appeared in 1,827 prior briefs since the 1970s, far more than the 896 Supreme Court appearances by attorneys filing briefs in support of the clinic.

Our research indicates that the Supreme Court produces opinions that borrow more from the briefs written by experienced attorneys than from the others. The court’s opinions are legal precedents that dictate the law in that area and define the decision’s impact. That happened in Dobbs; attorneys with more Supreme Court experience filed briefs that were more likely to be similar to the final opinions, while briefs by attorneys with less Supreme Court experience were less likely to resemble the final results.

These approaches may help us estimate results in upcoming cases

We can use these tools to examine upcoming cases as well. On Monday, the court will hear oral arguments in Sackett v. Environmental Protection Agency, which looks at the U.S. Court of Appeals for the 9th Circuit’s test for assessing whether wetlands fall under the Clean Water Act. Here, the sides are relatively balanced in both the information they provide and the resources they have available, although the petitioners — who seek a more restrictive understanding of the Clean Water Act — have a slight advantage.

As you can see in the figure below, the petitioners offer lengthier briefs, but those are not particularly novel. However, they do have more experienced attorneys.

On Tuesday, the court will hear arguments in Merrill v. Milligan, about an Alabama redistricting plan that the Northern District of Alabama ruled dilutes Black votes and therefore violates the Voting Rights Act. Here, the petitioners — who argue that the redistricting plan does violate the Voting Rights Act — offer the most information and are backed by more resources, as you can see in the next figure, with briefs supporting that are numerous, longer and less novel. (Perhaps counterintuitively, we have found that consistency among large groups of briefs — avoiding new arguments and coordinating among themselves — is a good sign for that side.) Although the court asks amicus filers not to repeat information found in other briefs, we, like other scholars, have found evidence that repetition helps that side. The petitioners, who oppose Alabama’s redistricting plan, also have more experienced attorneys.

The Supreme Court took a case on the EPA's authority that could undo most federal laws

Of course, the justices make their own decisions; they could well rule for the side that looks, to us, less fully briefed. And it’s also true that justices are influenced by their own ideologies — and that the Supreme Court tends to take cases to reverse lower courts’ rulings.

But the amount and kind of information flowing to the court, the attorneys’ levels of experience, and resources brought to bear in that litigation also matter. If our analysis is correct, observers might be surprised by this highly conservative court deciding in Merrill that Alabama has indeed violated the Voting Rights Act and must draw its district map all over again.

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Morgan L.W. Hazelton is an associate professor of political science and law (by courtesy) at Saint Louis University.

Rachael K. Hinkle is an associate professor of political science at the University at Buffalo, SUNY.

Together they are authors of Persuading the Supreme Court: The Significance of Briefs in Judicial Decision-Making (University of Kansas Press, 2022).

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