I don't think one can do a study using data exclusively from the University of California system and claim it applies to "research universities" in general. Notwithstanding New York, California is the current best example of a "liberal hellhole" state, so it would make sense that admission to that particular state's public university system is eventually associated with an increased left bent. Let's see this exact study methodology reproduced with e.g. Stanford admissions data where the Hoover Institution is a prominent presence, or the University of Mississippi/Alabama or Louisiana State University located in conservative hotbeds.