Scholars surveyed leading law professors as to which Supreme Court Justices they thought were great. Then the data was sliced up.
Even though this book is awfully short -- mostly tables -- it probably stretches a little more than it should. There's only so many times you can subdivide this data before it becomes meaningless.
The result is that they conclude things like "[I]f we were to describe the background of a typical Supreme Court 'failure,' . . . [h]is ethnic origins would be Scottish or Irish and he would be affiliated with a 'low church' Protestant denomination."
YIKES! Take it easy there, fellas.
What's more interesting is what the data says about (1) the people who responded to the survey and, (2) to a lesser extent, the selection process.