Decisions in the most contentious cases—those with one-vote margins—reveal much about a supreme court’s term. The number of cases, the issues involved, and the justices most often in majorities all attract attention. Numerous SCOWstats posts have explored aspects of these decisions, but never over an entire century. Today we do so, and the results are dramatic indeed.
One conclusion—that 4-3 decisions have become more abundant, and a larger percentage of all decisions in recent decades—could be extrapolated from previous posts and will not be our focus here. Instead, we’ll examine 4-3 majorities—in particular, the question of how many different combinations of justices made up 4-3 majorities in each term from 1917-18 through 2024-25. The findings illuminate such issues as polarization (and perhaps politicization) as the court navigated the 20th century and set out into the 21st.
The “polarization index”
To determine the polarization index for a term, take the number of 4-3 decisions and subtract the number of different 4-3 majorities. Then, divide the result by the number of 4-3 decisions.
For example, in 1922-23 there were seven 4-3 decisions with five different majorities, yielding a polarization index of (7–5)/7 or 2/7, which rounds to 0.286. After calculating the polarization index for each of the 104 terms, I multiplied them all by 1000 in order to remove the decimals.
In a nutshell, the polarization index measures how inclined justices are to vote in distinct blocs. When this happens less often—with justices regularly voting with different colleagues from one 4-3 case to another—the polarization index decreases. If every 4-3 decision during a term has a different majority, the index drops to zero. This occurred routinely during the first half century, as we shall see.
At the other extreme, the index approaches 1,000 as the quantity of 4-3 decisions expands and the number of different majorities remains small. In 2024-25, for instance, while the court filed only four 4-3 decisions, every one of them had the same majority—hence, a substantial polarization index of 750: (4-1)/4 x 1000. Consider also 2021-22, which generated an extraordinarily large volume of 4-3 decisions—28 in all—with only four different majorities: (28-4)/28 x 1000 = 857, the largest polarization index for any term.
Findings
Scrutinizing 4-3 majorities in this manner reveals increasingly rigid, entrenched voting blocs in the court over the past century—especially since 1970. From 1917-18 through 1969-70, the polarization index was never high and averaged only 102. From 1970-71 through 2024-25 it soared to 466, and for just the period 2020-21 through 2024-25 it reached 737.
Fully 59% of the 49 terms through 1969-70 had a polarization index of zero, including stretches of seven terms (1938-39 through 1945-46)[1] and five terms (1957-58 through 1961-62). After 1969-70, only four of 55 terms (7%) had polarization indices of zero.[2]
In 2023-24 and again in 2024-25 (each of which had four 4-3 decisions), the same four justices made up every 4-3 majority in the term. Never had this occurred previously in back-to-back terms. Indeed, only once before (1930-31) has there been even a single term with more than one 4-3 decision and with the same set of justices forming all the majorities.[3]
We can also view this transformation by calculating the average polarization index for each decade, as displayed in the following table.[4]
By 21st-century standards, 2014-15 and 2015-16 were unusual terms because each had a polarization index of zero.[5] However, even with their impact, the decade still posted an average polarization index of 331—much higher than for any decade prior to the 1970s.
If decade-long averages seem too rough a measure, we can compute five-term rolling averages—that is, the figure for each term consists of the average of the polarization indices for that term and the preceding four terms. This information, presented in the chart below, underscores how abruptly the index changed in the 1970s.[6]
(Click on the chart to enlarge it.)
Politicization
Many observers have viewed political considerations as ever more potent in shaping the Wisconsin Supreme Court. Few contend any longer that supreme court elections are non-partisan,[7] and the justices have appeared more disposed than in the early decades of our period to accept cases with an overtly political tinge.
It seems plausible to wonder if a connection exists between the profusion of polarized 4-3 majorities and the court’s emergent willingness to adjudicate politicized disputes. More research would be required to determine whether these two factors fed each other directly, or whether they were both swept along independently by a broader current, but they are surely not antagonistic phenomena.
That said, polarization and politicization need not march in lockstep, because a court can be polarized over issues lacking political spice. For instance, while polarized 4-3 majorities certainly surged at the beginning of the 1970s, as we have seen, did the court grow more politicized at the same time? This is difficult to establish conclusively, and I would welcome thoughts from readers whose institutional memory or scholarship permits comparison of, say, the mid 1960s with the early 1970s.[8]
Be that as it may, the court is emphatically more polarized by our measure early in the 21st century than it was a hundred years ago. However one regards this fact—a troubling consequence of mounting partisan rigidity perhaps, or possibly a salutary indication of judicial readiness to address more divisive issues—it remains a significant development.
[1] This interval also includes 1941-42, which had no 4-3 decisions.
[2] The four terms were 1980-81, 1995-96, 2014-15, and 2015-16.
[3] There were four 4-3 decisions in 1930-31.
[4] The “decade” of the 1920s runs from 1919-20 through 1928-29; the 1930s covers 1929-30 through 1938-39, and so forth.
Two of the terms in the 1920s (1927-28 and 1928-29) and two terms in the 1940s (1941-42 and 1947-48) had no 4-3 decisions, and these four terms are omitted in the calculations.
[5] The two terms reached polarization indices of zero in different ways—both of them abnormal in the 21st century. 2014-15 had only one 4-3 case. 2015-16 had seven 4-3 cases but with seven different majorities.
[6] The chart begins with 1921-22 because this is the first term to have four preceding terms in the period under consideration.
[7] The political analyst Craig Gilbert noted after this month’s supreme-court election that “[h]ow people vote in nonpartisan court races is increasingly tied to how they vote in partisan fall races. In recent decades, the relationship between voting patterns in April and voting patterns in November has gone from being very weak to very powerful. … Partisan intensity and partisan realignment are driving outcomes in court elections because almost everyone – voters, donors, the parties, advocacy groups – behaves now as if these were partisan elections.”
[8] Click here for a table providing the polarization index for each term in the 1970s and for a couple terms just before and after the decade. The table also lists the justices on the court during each term.
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