@article{Cragg1993,
author = {Cragg, J.G. and Donald, S.G.},
title= {Testing identifiability and specification in instrumental variables models},
year = {1993},
doi = {10.1017/S0266466600007519},
journal = {Econometric Theory},
volume = {9},
number = {2},
pages = {222--240},
}