TY  - BOOK
AU  - Rubin Donald B
AU  - Weisberg Sanford
TI  - Assessment of a treatment effect when a covariate is observed on a subset of the units : 1. simple estimators
U1  - 371.26 
PY  - 1974///
CY  - New Jersey
PB  - ETS
KW  - Educational tests and measurements
ER  -