Ideological leanings of U.S. Supreme Court justices
The U.S. Supreme Court is entrusted with resolving disputes about how the United States Constitution and other federal laws should be applied to cases that have been appealed from lower courts. The justices base their decisions on their interpretation of both legal doctrine and the precedential application of laws in the past. In a few cases, interpreting the law is relatively clear-cut and the justices decide unanimously without dissent. However, in more complicated or controversial cases, the Court is often divided.
It has long been commonly assumed that the votes of Supreme Court justices reflect their jurisprudential philosophies as well as their ideological leanings, personal attitudes, values, political philosophies, or policy preferences. A growing body of academic research has confirmed this understanding: scholars have found that the justices largely vote in consonance with their perceived values. Analysts have used a variety of methods to deduce the specific perspective of each justice over time.
Researchers have carefully analyzed the judicial rulings of the Supreme Court – the votes and written opinions of the justices – as well as their upbringing, their political party affiliation, their speeches, editorials written about them at the time of their Senate confirmation, and the political climate in which they are appointed, confirmed, and work. From this data, scholars have inferred the ideological leanings of each justice and how the justices are likely to vote on upcoming cases.
Using statistical analysis of Supreme Court votes, scholars found that an inferred value representing a Justice's ideological preference on a simple conservative–liberal scale is sufficient to predict a large number of that justice's votes. Subsequently, using increasingly sophisticated statistical analysis, researchers have found that the policy preferences of many justices shift over time. The ideological leanings of justices (and the drift over time) can be seen clearly in the research results of two sets of scholars using somewhat different models:
Andrew D. Martin and Kevin M. Quinn have employed Markov chain Monte Carlo methods to fit a Bayesian measurement model of ideal points (policy preferences on a one-dimensional scale) for all the justices based on the votes in every contested Supreme Court case since 1937. The graph below shows the results of their analysis: the ideological leaning of each justice from the term beginning in October 1937 to the term that began in October 2013. Note that the scale and zero point are arbitrary – only the relative distance of the lines is important. Each unique color represents a particular Supreme Court seat, which makes the transitions from retiring justices to newly appointed justices easier to follow. The black lines represent the leanings of the Chief Justices. The yellow line represents the estimated location of the median justice – who, as Duncan Black’s median voter theorem posits, is often the swing vote in closely divided decisions.
Michael A. Bailey used a slightly different Markov chain Monte Carlo Bayesian method to determine ideological leanings and made significantly different scaling assumptions. He analyzed cases by calendar year and supplemented the data regarding votes in each Court case with additional information from the majority, concurring, and dissenting opinions in which justices commented on previous cases, as well as with votes made by members of Congress on similar legislation, amicus filings by Solicitors General and members of Congress, and presidential and Congressional positions on Court cases. This additional information gave him a richer dataset and also enabled him to deduce preference values that are more consistent with the DW-Nominate Common Space scores used to evaluate the ideological leanings of members of Congress and Presidents. However, he only used votes and cases related to the major topics addressed by the courts in the postwar area: crime, civil rights, free speech, religion, abortion, and privacy. He did not include federalism or economic issues.
The graph below shows the ideological leaning of each justice by calendar year from 1950 to 2011. The scale and zero point roughly correspond to DW-Nominate Common Space scores, but otherwise are arbitrary. As in the graph above, each unique color represents a particular Supreme Court seat. The black lines represent the leanings of the Chief Justices. The yellow line represents the median justice.
These two graphs differ because of the choices of data sources, data coverage, coding of complicated cases, smoothing parameters, and statistical methods. Each of the lines in these graphs also has a wide band of uncertainty. Because these analyses are based on statistics and probability, it is important not to over-interpret the results. Still, they offer an indication of the overall ideological orientation of the justices and provide a way to visualize changes in the Court's orientation over time.
Ideological shifts since 1937
In the early 1930s (earlier than the data on the Martin-Quinn graph), the "Four Horsemen" (Justices James McReynolds, Pierce Butler, George Sutherland, and Willis Van Devanter) mostly opposed New Deal programs proposed by President Franklin D. Roosevelt. The liberal "Three Musketeers" (Justices Harlan Stone, Benjamin Cardozo, and Louis Brandeis) generally supported the New Deal. Two justices (Chief Justice Charles Evans Hughes and Justice Owen Roberts) stood in between.
As the Martin-Quinn graph shows, by the 1939 term, Roosevelt had moved the Court to a more liberal position by appointing four new justices including strong liberals Hugo Black, William O. Douglas, and Frank Murphy. However, led by the increasingly conservative Chief Justices Harlan Stone and Fred Vinson, the Court shifted in a more conservative direction through the early 1950s.
President Dwight Eisenhower appointed Earl Warren to be Chief Justice in 1953, and both graphs indicate that the Court then turned in a more liberal direction as Warren grew substantially more liberal and especially when he was joined by strong liberal justices William Brennan, Arthur Goldberg, Abe Fortas, and Thurgood Marshall (though Justices Black and Felix Frankfurter became more conservative over time).
In the 1970s, the Court shifted in a more conservative direction when President Richard Nixon appointed Chief Justice Warren Burger and strong conservative Justices Lewis Powell, William Rehnquist, and Harry Blackmun, and more so when President Ronald Reagan elevated Rehnquist to Chief Justice (though Blackmun became more liberal over time). The Court shifted to an even more conservative orientation when it was joined by strong conservative Justices Antonin Scalia, Clarence Thomas, Samuel Alito, and Chief Justice John Roberts (appointed by President George W. Bush), though Justice David Souter became more liberal over time.
Both graphs indicate that the current Roberts Court is quite conservative, with four very strong conservative justices (including Chief Justice Roberts) and the median position held by Justice Anthony Kennedy (appointed by President Ronald Reagan).
The most volatile seat appears to be Seat 10 (light blue lines) which was held by conservative Pierce Butler until 1939, then liberal Frank Murphy until 1949, then moderate-conservative Tom Clark until 1967, then strong liberal Thurgood Marshall until 1991, and then strong conservative Clarence Thomas. The path of Justice Harry Blackmun illustrates the ideological drift shown by many justices. Blackmun (purple line) had a conservative score (Quinn-Martin=1.890; Bailey=0.43) in the 1970 term, his first on the bench, but had shifted to a liberal score (Quinn-Martin=–1.860; Bailey=–0.81) by the 1993 term, his last. The median justice was Byron White for most of the time from 1970 to 1993, Sandra Day O’Connor from 1994 to 2005, and Anthony Kennedy since 2006.
- Supreme Court of the United States
- Segal-Cover score
- Judicial discretion
- Judicial activism
- Judicial restraint
- Segal, Jeffrey A.; Spaeth, Harold J. (2002). The Supreme Court and the Attitudinal Model Revisited. Cambridge: Cambridge University Press. ISBN 978-0521783514.
- Epstein, Lee; Martin, Andrew D. (2012). "Is the Roberts Court Especially Activist? A Study of Invalidating (and Upholding) Federal, State, and Local Laws". Emory Law Journal 61: 737–758. "…for Justices appointed since 1952, Epstein & Landes’s findings parallel ours: the vast majority were opportunistic restraintists (activists), willing to uphold laws that were consistent with their policy preferences and strike those that were not."
- Zorn and Caldeira provide a good overview of these methods and their limitations: Zorn, Christopher; Caldeira, Gregory A. (5 February 2008). "Measuring Supreme Court Ideology". Retrieved 30 November 2012.
- For example:
- Segal, Jeffrey A.; Cover, Albert D. (June 1989). "Ideological Values and the Votes of U.S. Supreme Court Justices". American Political Science Review 83 (2): 557–565. doi:10.2307/1962405. Segal and Cover found (p. 561) a strong correlation (0.80) between justices' perceived ideological perspectives on civil liberties and civil rights issues as attributed to them in elite newspaper editorials written just before their confirmation (their Segal–Cover score) and their later votes in the study period 1953–1988.
- Epstein, Lee; Walker, Thomas G.; Dixon, William J. (November 1989). "The Supreme Court and Criminal Justice Disputes: A Neo-Institutional Perspective". American Journal of Political Science 33 (4): 825–841. doi:10.2307/2111111. Epstein, Walker, and Dixon found they could explain and predict rulings in criminal justice cases (in the study period 1946–1986) using a simple model with four inputs: the political party affiliation of the majority of justices, the political party affiliation of the current president (representing the current political climate), the Supreme Court rulings in criminal justice cases in the previous year, and the percent of criminal cases the Court decides to hear in the current year (how much interest they take in the issue). In this analysis, the political party affiliation of the majority of justices provided about one-fourth of the predictive power.
- Pinello, Daniel R. (1999). "Linking Party to Judicial Ideology in American Courts: A Meta-Analysis". The Justice System Journal 20 (3): 219–254. Pinello conducted a meta-analysis of 84 studies of American courts covering 222,789 cases and found that political party affiliation was a dependable indicator of rulings: Democratic judges voted in favor of liberal solutions more often than Republican judges did, especially in federal courts (the U.S. Supreme Court, U.S. Courts of Appeal, and U.S. District Courts).
- Some examples:
- Grofman, Bernard; Brazill, Timothy J. (2002). "Identifying the median justice on the Supreme Court through multidimensional scaling: Analysis of 'natural courts' 1953–1991". Public Choice 112: 55–79. doi:10.1023/A:1015601614637. Grofman and Brazill performed multidimensional scaling (MDS) using SYSTAT 5.0 of the entire range of cases considered by the Supreme Court, 1953–1991. Analyzing terms with an unchanging membership ("natural courts") and a complete bench of nine members (3,363 cases), they found that a one-dimensional scale provided a satisfactory explanation of votes and that the degree of unidimensionality generally rose over the years. “On average, over the 15 courts, the mean r2 values are 0.86 for a one dimensional metric MDS solution, and 0.97 for a two dimensional metric MDS solution.”
- Poole, Keith (10 July 2003). "The Unidimensional Supreme Court". Retrieved 27 November 2012. "The bottom line is that the current Court is basically unidimensional." Poole used various statistical measures to show that a unidimensional scale provides a good measure of the Rehnquist Court during the 8-year period 1995–2002.
- Martin, Andrew D.; Quinn, Kevin M. (2007). "Assessing Preference Change on the US Supreme Court". The Journal of Law, Economics, & Organization 23 (2): 365–385. doi:10.1093/jleo/ewm028.
- Epstein, Lee; Martin, Andrew D.; Quinn, Kevin M.; Segal, Jeffrey A. (2007). "Ideological Drift among Supreme Court Justices: Who, When, and How Important?". Northwestern University Law Review 101 (4): 1483–1503.
- Ruger, Theodore W. (2005). "Justice Harry Blackmun and the Phenomenon of Judicial Preference Change". Missouri Law Review 70: 1209.
- Martin, Andrew D.; Quinn, Kevin M. (2002). "Dynamic Ideal Point Estimation via Markov Chain Monte Carlo for the U.S. Supreme Court, 1953–1999". Political Analysis 10 (2): 134–153. doi:10.1093/pan/10.2.134.
- Martin, Andrew D.; Quinn, Kevin M. (2 May 2001). "The Dimensions of Supreme Court Decision Making: Again Revisiting The Judicial Mind".
- Martin, Andrew D.; Quinn, Kevin M.; Epstein, Lee (2005). "The Median Justice on the United States Supreme Court". North Carolina Law Review 83: 1275–1322.
- Jackman provides a simple description of this kind of statistical analysis: Jackman, Simon (2011). "Statistical Inference, Classical and Bayesian". "International Encyclopedia of Political Science". doi:10.4135/9781412959636.n585. ISBN 9781412959636.
- "Martin-Quinn dataset".
- Silver, Nate (29 March 2012). "Supreme Court May Be Most Conservative in Modern History". New York Times. In his FiveThirtyEight blog, Silver graphed the Martin-Quinn data to show the movement of the median, most conservative, and most liberal justices over time.
- Black, Duncan (February 1948). "On the rationale of group decision-making". Journal of Political Economy 56 (1): 23–34. doi:10.1086/256633. JSTOR 1825026.
- Bailey, Michael A. (August 2012). "Measuring Court Preferences, 1950–2011: Agendas, Polarity and Heterogeneity". Retrieved 20 November 2012.
- Bailey, Michael A.; Maltzman, Forrest (2011). The constrained court: law, politics, and the decisions justices make. Princeton: Princeton University Press. ISBN 978-0691151052.
- Clinton, Joshua; Jackman, Simon; Rivers, Douglas (May 2004). "The Statistical Analysis of Roll Call Data". American Political Science Review 98 (2). doi:10.1017/S0003055404001194.
- Epstein, Lee; Martin, Andrew D.; Segal, Jeffrey A.; Westerland, Chad (May 2007). "The Judicial Common Space". Journal of Law, Economics, and organization 23 (2): 303–325. doi:10.1093/jleo/ewm024. "The [NOMINATE] Common Spaces scores are bounded below by -1 and above by 1, whereas the Martin-Quinn scores are theoretically unbounded (currently, they range from about -6 [Justice Douglas] to 4 [Justice Thomas])."
- Bailey, Michael A. (July 2007). "Comparable Preference Estimates across Time and Institutions for the Court, Congress, and Presidency". American Journal of Political Science 51 (3): 433–448. doi:10.1111/j.1540-5907.2007.00260.x.
- "Bailey dataset". Retrieved 22 November 2012.
- Ho, Daniel E.; Quinn, Kevin M. (June 2010). "How Not to Lie with Judicial Votes: Misconceptions, Measurement, and Models". California Law Review 98 (3): 813–876.
- Carroll, Royce; Lewis, Jeffrey B.; Lo, James; Poole, Keith T.; Rosenthal, Howard (November 2009). "Comparing NOMINATE and IDEAL: Points of Difference and Monte Carlo Tests". Legislative Studies Quarterly 34 (4): 555–591. doi:10.3162/036298009789869727.
- Liptak, Adam (24 July 2010). "Court Under Roberts Is Most Conservative in Decades". New York Times.
- Epstein, Lee; Landes, William M.; Posner, Richard A. (2013). "How Business Fares in the Supreme Court". Minnesota Law Review 97: 1431–1472. "We find that five of the ten Justices who, over the span of our study (the 1946 through 2011 Terms), have been the most favorable to business are currently serving, with two of them ranking at the very top among the thirty-six Justices in our study."