Treatment effect bounds

"We implement alternative bounding strategies to reanalyze data from the observational study by Connors et al. (1996) on the impact of Swan-Ganz catheterization on mortality outcomes. We implement both traditional bounds, which exploit access to an instrumental variable but impose no other assumptions (Manski, 1990), and the new bounds of Shaikh and Vytlacil (2004), which impose additional relatively mild nonparametric structural assumptions. Both of these approaches require an instrumental variable that shifts the probability of catheterization, but that does not alter mortality risks. We propose and justify using indicators of weekday admission as an instrumental variable in this context.We find that, while the traditional instrumental variable bounds are almost entirely uninformative in our application, the Shaikh and Vytlacil (2004) bounds often produce a clear answer - catheterization reduces mortality at 7 days, and increases it at 30 days and after. Our findings suggest an explanation for the fact that many ICU doctors are deeply committed to the use of the Swan-Ganz catheter. Since most ICU patients leave the ICU well before 30 days after admission have elapsed, ICU doctors never observe the increase in mortality. They do, however, observe the decline in mortality at 7 days"--National Bureau of Economic Research web site.