Adam Liptak NYT Sidebar column:

Political scientists say the conservative critique has a little merit, but not much. An analysis of voting patterns over the last decade shows Chief Justice Roberts to be well to the right of Justices Kennedy and Souter.

But a comparison of his votes with those of Justice Samuel A. Alito Jr., who was appointed by Mr. Bush in 2006, tells a slightly different story. The two started out ideologically indistinguishable. But Justice Alito has trended right, and Chief Justice Roberts left.

A recent study in The Journal of Legal Studies and related data presented an even more nuanced picture. It ranked the justices in ideological order and was prepared by Lee Epstein, a law professor and political scientist at Washington University in St. Louis; William M. Landes, a law professor and economist at the University of Chicago; and Judge Richard A. Posner of the United States Court of Appeals for the Seventh Circuit in Chicago.

They found that Chief Justice Roberts voted in a conservative direction 58 percent of the time over the last decade, while Justices Alito, Antonin Scalia and Clarence Thomas ranged from 61 to 65 percent.

But the chief justice leaned right when it mattered most. “He is a reliable conservative in the most closely contested cases but moderate when his vote cannot change the outcome,” the study said.

In 5-to-4 cases, the study found, Chief Justice Roberts voted in a conservative direction 85 percent of the time, a higher rate than that of any other member of the court.