As a general matter, the Justices that tend to carry the greatest ideological authority on the Supreme Court should be the ones authoring the greatest number of 5-4 opinions. Drafting those opinions shows that the senior justice in the majority either trusts the author to hold a majority or believes the author may only remain on that side if he or she writes the opinion. That begs the question: which Justice has written the greatest number of 5-4 majority opinions?

Average majority opinion authorship in 5-4 cases per term (OT 1996-Present)

Kennedy 3.50
Rehnquist 2.89
O’Connor 2.50
Scalia 2.36
Alito 2.0
Stevens 1.93
Thomas 1.93
Roberts 1.80
Souter 1.54
Breyer 1.50
Ginsburg 0.79
Sotomayor 0.0
Kagan 0.0

The liberal Justices’ low authorship rates are almost certainly due to their relatively low number of 5-4 victories over the past 15 years. Here is how the breakdown of total authorship looks by ideology:

Conservative author 105
Swing author 74
Liberal author 79
Total 258

Conservative Justices are Rehnquist, Roberts, Scalia, Thomas, Alito.
Swing Justices are O’Connor and Kennedy.
Liberal Justices are Stevens, Souter, Ginsburg, Breyer, Sotomayor, and Kagan.

However, not all 5-4 decisions split along traditional ideological lines. During that same time period, only about 70% of 5-4 decisions were divided along the traditionally easy-to-categorize ideological camps. The liberal Justices can’t blame all of their failure on swing voters, however, because 35% of ideologically divided cases still fell in their favor while 65% fell for the conservative Justices.

In order to adjust overall victories against the number of opinions authored, I also looked at how often a Justice would write the majority opinion as a percentage of their votes in the majority. For these numbers I only looked at OT 96-08, due to the absence of this data in SCOTUSblog’s OT 09 stat pack (please ignore the fact that the absence of that information is at least partially my fault).

Opinion authorship as a percentage of total votes in the majority (5-4 decisions, OT 1996-2008)

Justice Percentage Author Votes in Majority
Stevens 25.2% 26 103
Kennedy 25.1% 47 187
Rehnquist 23.4% 26 111
Scalia 20.0% 31 155
Breyer 19.6% 20 102
Souter 18.5% 10 108
O’Connor 18.1% 25 138
Roberts 16.7% 7 42
Thomas 16.0% 26 162
Alito 14.6% 6 41
Ginsburg 9.9% 10 101

Remember, in the absence of any political forces, each Justice would write the opinion in exactly 20% of the 5-4 cases where he or she was in the majority. A high ratio of majority opinions to votes in the majority could signal a Justice’s relative ideological strength. Justice Steven’s high opinion authorship ratio could be indicative of his role as the senior justice in any liberal 5-4 decision and his willingness to assign the opinion to himself in order to strategically retain the majority.

The two most obvious ways for a senior justice to assign the majority opinion in a tight case would be to either (1) assign the opinion to the swing justice or (2) assign the opinion to himself or herself in order to keep a majority. The fact that Justice Stevens probably presided over more tenuous 5-4 votes could explain his willingness to take one of the two obvious paths as opposed to the possibly less common route of assigning the opinion to another of the three justices in the majority.

Here are some of the best individual “performances” for a given term:

Justice Term Percentage Author Votes in Majority
Breyer 1999 75% 3 4
Stevens 2006 57% 4 7
Scalia 2005 50% 4 8
Kennedy 2007 50% 4 8

Bear in mind that some of these ratios may be SLIGHTLY off because majority votes are counted to include per curiam opinions but, obviously, no individual justice signed that opinion. I believe there were only 6 per curiam 5-4 decisions that were counted during the relevant period out of the 250 total 5-4 opinions counted.


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