Justice Sotomayor has completed two years on the Supreme Court and, as she begins her third, it seems like an appropriate time to take an initial look at whether or not she has turned out to be as predictably liberal as her supporters had hoped or as her opponents had feared. During her nomination, most expected her to be a moderately liberal vote, roughly in line with her predecessor, Justice Souter. After her first year, declared her to be a fairly reliable liberal vote, but there has been less analysis following her second year.

Well, not much has changed in her second year; Justice Sotomayor has proven to be roughly as liberal as expected. That isn’t surprising though, because Justices tend to act somewhat predictably during their first few years on the Court. If they do eventually diverge significantly from what their initial track record would support – à la Justices White or Souter – that drift isn’t typically apparent until a Justice has served for at least 3-5 years. Nonetheless, we can begin to analyze a Justice’s jurisprudence through a relatively small sample size with an eye towards future behavior. Here, I’ll look at three things: voting alignments, Martin-Quinn scores, and a few notable cases.

I. Voting Alignments

First, the easy part – statistics. Voting alignments show that Justice Sotomayor generally agrees with her liberal colleagues more than she does with the conservative ones. Below, I’ve listed her agreement rates with each of her colleagues in non-unanimous cases during OT09 and OT10.

Justice Sotomayor Voting Alignment – Non-Unanimous Cases – OT09 and OT10

Agreement in Full
Agreement in Part
Agreement in Judgment
Roberts 35 42%
38 45%
44 52%
40 48%
Stevens 25 60%
28 67%
29 70%
13 30%
Scalia 21 25%
28 33%
33 39%
51 61%
Kennedy 40 48%
41 49%
45 54%
39 46%
Thomas 21 25%
29 35%
34 50%
50 60%
Ginsburg 59 70%
61 73%
64 76%
20 24%
Breyer 56 68%
62 75%
65 78%
18 22%
Alito 23 28%
29 35%
37 45%
46 55%
Kagan 22 73%
25 83%
27 90%
3 10%

Note, of course, that Justice Sotomayor served only one term with both Justice Stevens and his successor, Justice Kagan. If you sort Justice Sotomayor’s ‘agreement in judgment’ rates, you can see a more vivid picture of the Court’s ideological split.

Agreement in Judgment with SMS
Kagan 90%
Breyer 78%
Ginsburg 76%
Stevens 69%
Kennedy 54%
Roberts 52%
Alito 45%
Thomas 40%
Scalia 39%

There isn’t much to say here except that, although Justice Sotomayor and Kagan had a remarkably high agreement rate in non-unanimous cases during OT10, they still had only the second-highest rate of the term. Chief Justice Roberts and Justice Alito agreed in judgment in 93% of all divided cases.

II. Martin-Quinn Scores

Martin-Quinn scores generally track a Justice’s ideology across a variety of areas in the law. A negative score indicates a “liberal” voting history and a positive score indicates a “conservative” voting history. Over the past two years, Justice Sotomayor has clearly fallen left of the median on the Court.

Average MQ Score (OT09 and OT10)

Average Score
Thomas 4.039
Scalia 3.054
Alito 2.467
Roberts 2.252
Kennedy 1.336
Kagan* 0.029
Sotomayor 0.019
Breyer -0.043
Ginsburg -0.092
Stevens** -0.632

*Served only during OT10
**Served only during OT09.

The most interesting aspect of MQ scores is that they purport to compare Justices across different generations. As you can see below, even the most “liberal” members of the current Court are relatively moderate by historical standards.

During OT09 and OT10, the Court (Sotomayor excluded) averaged 1.589. Sotomayor was therefore 1.570 below the mean. As you would expect, however, she is also just marginally more conservative than Justices Ginsburg, Breyer, and, her predecessor, Justice Stevens.

III. Notable Cases

Sotomayor is a reliable liberal vote, both generally and in the most high-profile cases. The statistics above provide support for her consistency in most cases, and a look specifically at the high-profile cases during OT09 and OT10 reveals the same trend. In McDonald v. Chicago, Salazar v. Buono, Citizens United v. FEC, Free Enterprise Fund v. PCAOB, Brown v. Plata, and AT&T v. Concepcion, she voted with the liberal bloc of the Court. Even in quirky cases like Bullcoming v. New Mexico, she seems to have assumed the same general position as her predecessor.

Her most notable betrayal was not much of a betrayal at all. In Sorrell v. IMS Health, Justice Sotomayor joined a five-justice conservative majority in striking down a Vermont law the regulated the distribution of prescription drug information.

IV. Conclusion

I wish there was shocking news to report, but there simply is not. After two years on the Court, Justice Sotomayor is just as liberal as expected, and she seems to have settled into her role rather comfortably. Cases like Sorrell suggest a willingness to deviate when necessary, but she clearly has not felt the need to break rankings with any measurable frequency.

5 Responses to “Measuring Justice Sotomayor’s Liberal Bona Fides”

  1. 1 Gary Peter Klahr,J.D.

    My concern is that in criminal cases, like oither recent liberal justices, SMS is no Brennan/Warren/Blackmun liberal. She proved such on the 2nd Circuit. She will be as liberal as Souter, who turned out to be a surprise-liberal as did Blackmun –the same as White surprised all of us by being a surprise conservative. I guess we can’t complain because Ike unintentionally gave us liberals like Brennan & Warren.

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