@article{Levin2002,
author = {Levin, A. and Lin, C.F. and Chu, C. },
title= {Unit root test in panel data: Asymptotic and finite sample properties},
year = {2002},
doi = {10.1016/S0304-4076(01)00098-7},
journal = {Journal of Econometrics },
volume = {108},
number = {1},
pages = {1--24},
}