The U.S. Supreme Court Building is on Capitol Hill in Washington. (AFP/Karen BLEIER)

How does an eight-member Supreme Court differ from one with the full complement of nine justices? So far this year, we’ve seen an important case — Friedrichs v. California Teachers Association — deadlocked, leaving the appeals court decision in place. In another key case, Zubik v. Burwell, the justices sent the issue back to the lower courts.

But there’s more to the answer. A shorthanded court is likely to hear fewer cases than normal. And that’s exactly what we’re seeing, with the court on track to take fewer cases for next year than it has in nearly 70 years. Although the court’s caseload has been falling since the 1980s, the justices have scheduled just 13 cases for oral argument next term. Usually, by this point in the calendar year, the court has scheduled an average of 18 cases.

Our research suggests that this drop is happening because the justices on an eight-member court are not sure how decisions would play out.

Here’s how we analyzed this.

In a recently published article in Justice System Journal (co-authored with Karen Miranda), we used the Supreme Court Database to measure the size of the court’s docket and the votes on each case between 1946 and 2005. In the figure below, we show the size of the caseload through 2015 and also include the announced 2016 docket.


Sources: Supreme Court Database (1946 through 2014 terms) and ScotusBlog (2015 and 2016 terms).
Figure created by the authors.

Four justices must agree to hear a case; otherwise, it does not get on the docket.

Here’s the hypothesis: If justices cannot predict with any degree of certainty what the outcome will be if they decide to hear a case, they become more reluctant to agree to hear the case. After all, although justices might want to affirm a lower court case they like, or strike down a lower court case that they think was decided incorrectly, they don’t want to roll the dice if uncertain about their colleagues — only to have the court overturning a favorable lower court decision or approving an unfavorable one.

If justices vote to hear a case based in part on what they think their colleagues will do, then the more certain they are about the likely outcome of a case and that their preferred side will win and the more likely they are to vote to hear a case. In other words, they are more likely to hear cases when they believe they will be a part of a stable winning coalition.

To test this, we collected each justice’s vote on each case, and calculate the percentage of the time that the five justices who most frequently voted together in each term actually did so. If our hypothesis is correct, when this percentage is higher and the winning coalitions are more stable, then justices are more certain about case outcomes — and more likely to take more cases. But when there’s not a stable winning coalition, justices will vote to hear fewer cases, since they can’t predict the outcomes.

When the court has a stable winning coalition, it takes more cases — and when it doesn’t, it takes fewer

And that’s what we found. During the 1983 term, for example, the five justices who voted most frequently together did so nearly 70 percent of the time. The court heard 150 cases in the next term. During the 2001 term, though, the justices who voted most frequently together did so only 57 percent of the time. And the court heard only 75 cases in the next term.

In other words, our results supported the hypothesis. When there are stable winning coalitions involving five or more members, justices vote to hear more cases.

But when the court does not have a stable winning coalition, it takes fewer cases. That’s where the court finds itself today: with an even ideological split. With only eight justices — divided between four liberals and four conservatives — the likelihood of one side winning is highly uncertain. So we should not be surprised that the court is taking fewer cases for next term, waiting until a new coalition settles down, presumably after a new justice is at last confirmed.

Of course, that’s not the only reason the Supreme Court hears fewer and fewer cases

A 1988 law, the Supreme Court Case Selections Act, gave the court discretion over whether to hear appeals from circuit court decisions. This gave the court more latitude over its caseload than it previously had, freeing it from hearing many cases that it previously was mandated to hear. Ryan Owens and James Simon showed this effect in an analysis similar to ours.

We also found that when the court’s ideological orientation is very different from that of Congress and the president, it will hear fewer cases, hoping to avoid negative attention from these elected politicians. More specifically, using ideology scores for these institutions created by Mike Bailey, we examined a court that is ideologically out of step with Congress and the president — for example, a conservative court that faces a Democratic president and a Democratically controlled Congress — and found that in such circumstances the court hears fewer cases.

Although this is not the current arrangement of preferences, this hypothesis provides a strong explanation for historical differences in the size of the court’s docket — and shows another way in which the justices act strategically.

But the uncertainty associated with future rulings seems to be central to the court’s current behavior. Justices would rather the lower courts decide important cases like Zubik v. Burwell than risk rulings that, in their view, could be disastrous nationally.

Recently, Vice President Biden quoted former justice Antonin Scalia by stating that a court with eight justices hearing a case “will find itself unable to resolve the significant legal issues presented by the case.”

Does this make the court less powerful — and if so, is that good or bad? Reasonable observers will differ. What we do know is that when the result is uncertain, the court hears fewer cases. For good or for ill, that’s one more repercussion of a short-handed court.

Kenneth W. Moffett is associate professor of political science at Southern Illinois University Edwardsville.

Charles R. Shipan is J. Ira and Nicki Harris Professor of political science at the University of Michigan.

Forrest Maltzman is professor of political science at George Washington University.