Roberts the Rebel?

From Born to Rebel: Birth Order, Family Dynamics, and Creative Lives: "Relative to firstborn justices, laterborn justices have been significantly more likely to vote in a liberal direction." This review of the book in Scientific Exploration also points out that Republican presidents nominate more first-born justices than do Democratic presidents.

Does this mean that the Roberts Court will tilt unexpectedly to the left? Justice Alito (as a first born child) should be no more liberal than Justice O’Connor (also a first born); but Chief Justice Roberts (only the second oldest of four) may be ever so slightly more liberal than the late Chief Justice Rehnquist (the oldest of two).