At the end of every judicial year, statistics are produced about who agreed with who the most and so on. These statistics are incredible useful for almost every Supreme Court question imaginable!
The way in which Justices vote in a case is a huge part of the study of the Supreme Court. This article looks at the purported unanimity of the most recent Supreme Court year and argues it is not as clear cut as it seems.
Two-thirds of the decisions this year have been 9-0 decisions; unusually high. However, the written decisions do not reflect total agreement. Supreme Court Justices write a number of decisions at the end of a case: the ‘majority’ decision (the winning decision), the ‘dissent’ (the losing decision, if it’s not unanimous) and ‘concurrent’ decisions. ‘Concurrent’ decisions are basically additions, a justice add his or her own personal opinion either to the majority or dissenting opinion. This gives Justices an opportunity to explain that, while they may agree or disagree with a case, that they do so for different reasons to their colleagues.
The Obamacare case is a great example (NFIB v Sebelius). The majority was Chief Justice John Roberts plus the 4 ‘liberal’ justices on the court and the majority decision was that Obamacare was not a tax. However, in his concurrent opinion, the Chief Justice outlined that while constitutionally Obamacare was not a tax, he disagreed with Obamacare constitutionally for many more reasons. Therefore while the ‘majority’ appear to agree, in reality it was not so clear.
This article explores this in a little more detail and is fantastic! For a somewhat more analytical look, I also recommend: http://www.washingtonpost.com/politics/courts_law/for-these-supreme-court-justices-unanimous-doesnt-mean-unity/2014/07/01/94003590-0132-11e4-b8ff-89afd3fad6bd_story.html?wpisrc=nl_pmpol