TY  - BOOK
AU  - Heckman, JJ
AU  - National Bureau Of Economic Research
TI  - Econometric Mixture Models And More General Models For Unobservables In Duration Analysis
T2  - Techinical Working Paper Series
U1  - NBER TWP157 
PY  - 1994///
CY  - Cambridge, MA
PB  - NBER
ER  -