Stras and Scott have written An Empirical Analysis of Life Tenure: A Response to Professors Calabresi & Lindgren. The Abtsract:
"Opposition to life tenure has been steadily mounting in the legal academy and Professors Steve Calabresi and Jim Lindgren are among those leading the charge. Crucial to their argument that life tenure is "fundamentally flawed" is an empirical claim that the increases in average tenure among Supreme Court Justices are both "dramatic" and 'unprecedented."
In this article, the authors respond to Calabresi and Lindgren by showing that their hypothesis of dramatic and unprecedented growth in average tenure has two fundamental flaws. First, it suffers from a period-selection problem. Rendering the data using longer or shorter periods blunts or eliminates the dramatic and unprecedented trend. Second, it suffers from a date-of-observation problem. Treating each Justice's tenure as an observation at date of swearing-in (or at the midpoint of a Justice's career), rather than at date of departure, eliminates the trend altogether. Instead, the authors show that, using an S-curve regression model, the most supportable hypothesis is that, despite short-term fluctuations, average tenure has been growing slowly and steadily over the long term, and we can expect more slow and steady growth in the future."