Their chart on agreement over all cases for the October term, 2012, tells us that the justices agree more often than not. For example, Scalia agreed with Ginsburg (in full, part, or in the judgment only) a full 74% of the time while Roberts’s lowest agreement rate with any judge was 71%. The lowest agreement rate between any two justices was that of Alito and Sotomayor at 64% while the highest agreement rate overall was 97% between Sotomayor and Kagan.
But it may be more interesting to consider how they line up on divided cases and 5-4 cases. As for divided cases, the pairs of Sotomayor & Kagan, Sotomayor & Ginsburg, and Kagan & Ginsburg agreed between 89.7% and 93.2% of the time. The three lady justices had 100% agreement on the 5-4 decisions.
The highest agreement level from the other wing of the court was between Roberts and Alito, who were together on 75.9% of divided cases and 100% of the 5-4 decisions . Roberts and Thomas agreed on 70% of divided cases and 86.7% of 5-4 decisions. Scalia and Thomas had what is for many the surprisingly low agreement rate of 70% on divided cases and 73.3% of 5-4 decisions.
Overall the most diametrically opposed justices are Alito over against Sotomayor, Ginsburg, and Kagan, with no more than 21.4% agreement between Alito and any of them on divided cases and 0% on 5-4 decisions. Other notable disagreements are Thomas against the lady justices and Scalia against Breyer, the latter two having had only 27.6 % agreement on divided cases and 0% on 5-4 decisions.
On the whole the data shows consistent agreement among Sotomayor, Kagan, and Ginsburg with Breyer not far out of step. The other alignment is Alito, Roberts, Thomas, and Scalia. Conspicuously missing from the chart of most extreme agreement rates is Justice Kennedy, who must get a lot of attention from his colleagues while close decisions are being discussed.