This paper is very clever:
Health care spending varies widely across markets, yet there is little
evidence that higher spending translates into better health outcomes,
possibly due to endogeneity bias. The main innovation in this paper
compares outcomes of patients who are exposed to different health care
systems that were not designed for them: patients who are far from home
when a health emergency strikes. The universe of emergencies in Florida
from 1996-2003 is considered, and visitors who become ill in
high-spending areas have significantly lower mortality rates compared
to similar visitors in lower-spending areas. The results are robust
across different types of patients and within groups of destinations
that appear to be close demand substitutes.
Here are non-gated versions.