In an interesting article on FiveThirtyEight called “Supreme Court Justices Get More Liberal As They Get Older,” the author Oliver Roeder analyzes the changes in the opinions of the justices as they grow in age. He writes that while for most people there is a change from liberal to more conservative as aging occurs, the opposite is true for the justices. Roeder uses a measure called the Martin-Quinn score to illustrate this change in ideology. The score uses the votes of the justices to map them onto a left-right spectrum. A positive number means the person has shifted more to the right while a negative score means a person has grown more liberal.
Roeder provides a plot showing the changes in all of the justices’ ideologies since the 30’s. He also uses a best fit line to map these results in an easy to analyze line. It is clear from the graph he uses that over time both justices nominated by Democrats and by Republicans have grown more liberal as they have aged in recent years. He uses a second, similar graph to further support his case with only the nine current justices being graphed. For nearly every justice, they have grown more liberal as they have gotten older. Reorder uses these two graphs to make a very convincing case for the leftward-drift of ideology of the justices as they have gotten older, a shift that is the opposite of what is typical for most citizens.