Scholars studying Congress often keep track of the frequency of "party-line" votes, which occur when the vast majority of both parties vote together and in opposition to one another. This happened with the Affordable Care Act in 2010, when every single Democrat voted “yes” and every single Republican voted “no.” Party-line votes are an increasingly common phenomena in Congress, symbolizing its growing polarization.

The same concept of voting along party lines can be applied to the court, providing the most accurate test for polarization levels. For the purposes of this study, I’ve defined a Supreme Court party-line vote as when each of the liberal justices and each of the conservative justices cast opposing votes on a case.

To measure ideology, I used Martin-Quinn Scores,which are commonly used to classify justices as conservative or liberal. It should be noted that these scores are not stagnant; justices receive new Martin-Quinn Scores each term, meaning a justice could be classified as conservative in some terms and liberal in others (of course, this would be rare...unless you’re Justice Kennedy).

So are party-line votes in the Supreme Court becoming more common over time?