a methodology difference between conservatives and liberals...
http://www.usnews.com/articles/news/national/2008/05/12/ranking-the-politics-of-supreme-court-justices.html
"The more conservatives join a conservative court, the more conservative each [conservative] justice gets. The
same thing doesn't appear to be true, curiously, for left-leaning
judges. The authors find that the court's liberal justices are driven
to vote more ideologically not when their numbers grow but when they
begin to drop. The fewer justices there are on the court appointed by
Democratic presidents, in other words—meaning the more outnumbered the
liberal justices are—the more liberal those justices get."
