TY  - JOUR
A1  - Heckman, J.
A1  - Urzua, S.
A1  - Vytlacil, E.
T1  - Understanding instrumental variables in models with essential heterogeneity
Y1  - 2006
DO  - 10.1162/rest.88.3.389
JF  - Review of Economics and Statistics
VL  - 88
IS  - 3
SP  - 389
EP  - -432

ER  -