Picking up on the methodological contribution I think psychology can make to ELS, it seems as though psychology emphasizes experimental work to a greater degree than current ELS. Discussing the excellent methodology workshop that Lee Epstein and Andrew Martin run, someone recently joked that it covers 95% of all the methodology ELS scholars need to know. I’d quibble with that if, as I understand (without having attended), there’s little coverage of experimental design and analysis (e.g., analyses of variance or ANOVA’s). To be very clear, all I mean by that is I think the experimental approach could be a larger proportion of ELS work than it currently is.
Experimental research, of course, can contribute greatly to our understanding of a number of topics and phenomena (jury understanding of sentencing instructions; eyewitness accuracy; racial discrimination by judges and jurors; effects of policy interventions; different influence of legal procedures both in and out of the courtroom, etc., etc.). Researchers can manipulate specific variables and test their causal effect, tweaking particular aspects to really parse out specific effects that may be more precise than multiple regression. In some instances – when a researcher is working with existing databases – experiments can be less constrained by data limitations, can be more proactive in data collection.
Among the downsides, of course, is the perception that experiments aren’t “externally valid” – they don’t sufficiently reflect the real world that we can profitably generalize. Sometimes, true. But they sometimes do, and sometimes can be conducted in real-world settings. Other times, finding an effect in the lab suggests it might be even stronger in the real world: the example often given is with comprehension of capital sentencing instructions – when highly educated mock juror subjects from “elite universities” don’t understand them, how much more of a concern might it be for less educated jurors faced with such instructions in the real world? In yet other contexts, again with mock juries, differences between undergraduate samples and community member samples are substantially less than critics have suggested (Bornstein, 23 Law & Hum. Behav. 75 (1999)).
I don't want to oversell the experimental approach, but it could certainly be another arrow in the ELS quiver. So to speak.