From the abstract:
In contrast to the traditional political science view, which holds that justices on the left are more supportive of free speech claims than justices on the right, and in contrast to a newer view among legal academics that justices on the right are more supportive of free speech claims than justices on the left, we use in-group bias theory to argue that Supreme Court justices are opportunistic supporters of free speech. That is, liberal (conservative) justices are supportive of free speech when the speaker is liberal (conservative).
A two-level hierarchical model of 4,519 votes in 516 cases confirms the in-group bias hypothesis. Although liberal justices are (overall) more supportive of free speech claims than conservative justices, the votes of both liberal and conservative justices tend to reflect their preferences toward the speakers’ ideological grouping, and not solely an underlying taste for (or against) the First Amendment.
Click here for a summary of the findings prepared for the New York Times
Click here for the data (Stata .dta file) (posted on May 2, 2014) (an Excel file is here)
In Justices’ Votes, Free Speech Often Means ‘Speech I Agree With’
Source: Adam Liptak, New York Times, May 5, 2014