Brian Broughman and Deborah Widiss have posted this draft on SSRN. Here is the abstract:
The ability of Congress to override judicial interpretations of statutory language is central to legislative supremacy. Both political science and legal scholarship assume, often implicitly, that enactment of a legislative override will effectively replace the pre-existing precedent, akin to a judicial overruling of a prior decision. Yet, because the superseding language comes from Congress rather than the courts, it is often unclear precisely how an override interacts with the pre-existing precedent. Our study is the first to empirically address this issue. We built an original dataset of annual citations to three different groups of Supreme Court decisions: (i) cases overridden by Congress (ii) cases subsequently overruled by the Court, and (iii) a matched control group of Supreme Court decisions that were neither overridden nor overruled. Using fixed effect regression analysis, we find that, on average, citation levels to cases that have been at least partially superseded — what we call “shadow precedents” — decrease only minimally after an override, while they decrease dramatically after a judicial overruling. Our results suggest that when faced with competing signals from Congress and the courts above them, trial courts look for interpretive guidance from other judicial actors, and that courts often continue to rely extensively on overridden precedents.