How To Analyze Data: 21 Graphs that Explain the Same-Sex Marriage Case, Public Opinion, & Supreme Court

Part 2: Politics & Why Justice Kennedy’s Opinion Matters

Overturn Percentage

The Court has an average overturn percentage of 0.65% over the last 60 years. This makes sense: the Justices do not need to affirm a case if the finding was the right one. In this case, the Justices are responding to four opposing Federal Court decisions about same-sex marriage bundled into one. This type of lower court disagreement is known as a “circuit split”. The Justices could affirm parts of the lower court decisions–ruling that the lower courts made the right decision on same-sex marriage–or, the Justices could overturn the lower court rulings and make their own.

Vote Distributions

In this case, analysts believe that the views of Justice Kennedy (pictured above) will take the day in a 5-4 split. In general though, unanimous decisions are about twice as likely as a 5-4 split. For more, see this paper on the “Statistical mechanics of the US Supreme Court.”

Ideological Spectrum of Supreme Court Justices

Another theme of recent scholarship is an ideological shift to the conservative side. For example Martin and Quinn argue that “Between 2005 and 2010, most of the the Roberts’ court five conservative-leaning members became more so.”

Supreme Court Decisions & Public Opinion

Public opinion is less important for a lifetime judge than an elected official. The Court hasn’t always done what is popular with the general public. Support was meager, at best, for decisions regarding interracial marriage, flag burning, and prayer in school.

The Ideology Behind Justice Decision Making

The median Justice casts the deciding vote in a 5-4 split. Kennedy can side with the liberals (Ginsburg, Breyer, Sotomayor, Kagan–Clinton and Obama appointees) or conservatives (Scalia, Thomas, Roberts, Alito–Reagan, Bush Sr. & Jr. appointees). His vote swings the Court, deciding who wins. The graph below shows how each Justice’s ideology relates to the views of the median Justice.

Part 3: The Justices, Clerks, & Public Opinion

Ages, Tenure, & Appointments

Justices serve for life, allowing a President to influence the Court through a nominee well past their time in office (though not always as they hope to). As President Obama noted:

Of the many responsibilities accorded to a President by our Constitution, few are more weighty or consequential than that of appointing a Supreme Court Justice.

This plot shows the average age and length of tenure of the Justices. Both decrease during the years when new justices are appointed (since new justices are typically younger than the existing justices).

Justice Support

The Justices fare well when it comes to nominee approval during confirmation votes. One study’s data shows that state support for nominees sways Senate votes. The solid vertical line indicates the mean level of state support.

The Political Positions of Media

Certain Justices align more closely with certain media outlets, as shown by Ho and Quinn’s figure. The median positions of the justices have been superimposed for comparison in the bottom panel with lines extending into the top plot to compare their views. The gray density presents the unweighted dentisty. The black line presents the density weighted by circulation, with the bump on the right representing the Wall Street Journal. 52% of the papers examined in the study have political positions between the 4th (Breyer) and 6th (Kennedy) Justices. The authors concluded:

In essence, there appear to be four clusters of newspaper positions corresponding to moderate and more extreme liberal and conservative positions. Of particular interest is the fact that even the more moderate papers cleave into left-leaning and right-leaning variants.

Where Clerks Come From

Supreme Court Clerks play a key role in assisting the Justices with opinions and choosing which cases the Court will hear. When the Justices choose clerks, they often do so from feeder judges for whom clerks previously worked at the Federal level. These judges are appointed by Republicans or Democrats, and increasingly serve as direct pipes to similarly-minded Justices. The Times concluded:

The conservative half of the court overwhelmingly hires clerks who served judges appointed by Republican presidents, while the liberal half of the court is more likely to hire clerks from judges appointed by Democrats, a pattern that was not as strong 30 years ago.

Supreme Court Public Approval

The Court, like the decisions it makes, isn’t always popular. A recent Gallup poll reveals that the public approval rating of the Supreme Court has decreased since 2010.

Pace of Decisions

The Court typically releases more opinions near the end of the term in June (OT stands for “October Term”). The plot below shows the average number of decisions released by the Court per year throughout their term. The data was compiled by SCOTUSblog. The end of the term is usually when the Court releases larger decisions. Now all we can do is wait and see.

How We Made These Plots & How You Can Too

Plotly lets you make and embed graphs in your website, blog, or application. It’s easy:





We made this post with a blend of our our web application–where you can upload files and graph data from a spreadsheet–and our APIs for R, Python, & MATLAB. We’re @plotlygraphs, or email us at feedback at plot dot ly. To learn more about how companies are using Plotly Enterprise across different industries, see our customer stories.