Beyond replication: A few comments on Spruk and Kovac and Martin-Quinn scores

Abstract

This Comment discusses Spruk and Kovac’s (2020) replication and extension of a prominent judicial ideology measure, the Martin-Quinn (2002) scores. Spruk and Kovac’s main contribution is to replicate Martin-Quinn scores’ Justice-level ideal points incident to a slightly different empirical strategy. Spruk and Kovac then extend their analysis by exploiting another prominent data set, Spaeth et al.’s (2018) Supreme Court Database, and identifying specific case issue codes that account for a large share of the Justice ideal points’ variation. For reasons that I outline below, while the Spruk and Kovac paper largely achieves its immediate replication objectives, the paper’s extension effort, by contrast, confronts inevitable limitations necessarily imposed by the Spaeth et al. database.