In a recent paper, Dawn of the Discipline-Based Law Faculty, Lynn LoPucki (UCLA) documents the sharp increase in entry-level hires possessing PhDs at AALS-member law schools between 2011 and 2015. According to Stephen Bainbridge (UCLA), who "deplores" this trend, "LoPucki believes the trend in favor of PhD law professors has reached a point of no return, potentially cementing a future where law school faculty, are long on degrees and publications—but short on time outside university walls." Brian Leiter (Chicago) has also recently weighed in on this trend, and his take is a bit more measured and detached: "Although I'm quoted saying that the rise of JD/PhDs will continue, that's a descriptive not normative statement. I think different schools have different missions. And the relevance of the JD/PhD varies by field."
While the rise in empirical legal scholarship and the concurrent increase in law faculty possessing a JD/PhD combo are distinct, to ignore how these two trends interact is to blink at reality. As such, legal empiricists need to be mindful of these critiques.
UPDATE: Readers pointed me to another recent paper, The Ph.D. Rises in American Law Schools, 1960-2011: What Does It Mean for Legal Education?, by Justin McCray (Berkeley) et al. In it, the authors study faculty hiring at the 34th highest-ranked law schools between 1960-2011. After documenting a rise in PhD hiring, the authors note that "the shift toward Ph.D.s entails a complex set of benefits and costs for law schools, and that there is the potential for building connections between practical experience and academic research, rather than simply choosing between them."