James J. Heckman, Sergio Urzua, Edward Vytlacil, Understanding Instrumental Variables in Models with Essential Heterogeneity, The Review of Economics and Statistics ...

James J. HECKMAN, Sergio URZUA, Edward VYTLACIL, Instrumental Variables in Models with Multiple Outcomes: the General Unordered Case, Annales d'Économie et de Statistique, No. 91/92, Econometric ...

RESULTS: Among 6,232 elderly patients, the instrumental variable estimate indicated an increase in median survival of 33 days and an improvement in 1-year survival of 9% attributable to chemotherapy.