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

May 21, 2015
By

(This article was first published on Plotly Blog, and kindly contributed to R-bloggers)

The nine Justices on the United States Supreme Court recently took up a case about same-sex marriage. The question in Obergefell v. Hodges is whether states are required to license and recognize marriages between two people of the same sex. This post examines the same-sex marriage case and Court in three sections about:

  • Public opinion on same-sex marriage (10 graphs)
  • Politics and voting on the Court (5)
  • Justices, clerks, & opinions about the Court (6)

We made these graphs with our free online tool; contact us to use Plotly Enterprise on-premise.


Part 1: Public Opinion

Opinion Over Time

According to Pew, Americans opposed same-sex marriage by a 57% to 35% margin in 2001. Today 52% support same-sex marriage and 40% oppose it. Pew reports a 95% confidence interval with a margin of error of 2.4%, represented here with error bars.

Americans Who Support/Oppose Same-Sex Marriage" style="display: block; text-align: center;">Americans Who Support/Oppose Same-Sex Marriage" style="max-width: 100%;width: 800px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

A Look At The Big Polls

The shift in public opinion is the story of recent polling on same-sex marriage. Made with R, the plot below shows the trend: Approval for same-sex marriage has moved above 50% in multiple polls in the past five years.

Same-Sex Marriage Approval By Polling Group" style="display: block; text-align: center;">Same-Sex Marriage Approval By Polling Group" style="max-width: 100%;width: 779px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

Sparklines & Demographics

Here we can see the change broken down by demographics in sparklines. Hover your mouse to learn more.

Same-Sex Marriage: % Who Support..." style="display: block; text-align: center;">Same-Sex Marriage: % Who Support..." style="max-width: 100%;width: 800px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

Attitudes by Generation

Younger generations are more supportive of same-sex marriage. Older generations have shifted their opinions in recent years.

How Generations View Same-Sex Marriage..." style="display: block; text-align: center;">How Generations View Same-Sex Marriage..." style="max-width: 100%;width: 800px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

Attitudes by Religious Affiliation

A majority of religiously unaffiliated individuals have supported same-sex marriage since 2001. Support for same-sex marriage has also increased among Catholics, white mainline Protestants, and black Protestants.

How Religions View Same-Sex Marriage..." style="display: block; text-align: center;">How Religions View Same-Sex Marriage..." style="max-width: 100%;width: 800px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

Attitudes by Political Ideology

75% of self-described liberals and 62% of moderates support same-sex marriage.

Attitudes by Political Ideology" style="display: block; text-align: center;">Attitudes by Political Ideology" style="max-width: 100%;width: 800px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

Attitudes by Political Party

64% of Democracts favor same-sex marriage, as do 58% of independents. Most Republicans oppose same-sex marriage.

Attitudes by Political Party" style="display: block; text-align: center;">Attitudes by Political Party" style="max-width: 100%;width: 800px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

Attitudes by Gender

Today 55% of women and 49% of men support same-sex marriage.

Attitudes by Gender" style="display: block; text-align: center;">Attitudes by Gender" style="max-width: 100%;width: 800px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

Attitudes by Race

53% of whites and 42% of blacks support same-sex marriage.

Attitudes by Race" style="display: block; text-align: center;">Attitudes by Race" style="max-width: 100%;width: 800px;" width="450" onerror="this.onerror=null;this.src='https://plot.ly/404.png';"/>

Public Opinion Box Plot

This box plot shows the spread in opinion for each year from 2001-2014. The box shows the distribution of opinions, allowing us to see how values vary within and compare between groups. Note the spreads. For example, moderates reported a 34% approval low in 2004 and a 64% high in 2014. Others have not moved or spread as much (e.g., White Evangelical Protestants changed by 10%). The data below come from Pew polling (see questions here and methodology here).

Same-Sex Marriage Support, 2001-2014

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.”

Supreme Court Decision Data

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.”

Justice Ideological Spectrum

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.

Justice Decision Making Ideology

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.

Political Positions of the Media

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.

Supreme Court Approval

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.

To leave a comment for the author, please follow the link and comment on their blog: Plotly Blog.

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