@article{Maddala1999,
author = {Maddala, G.S. and Wu, S.},
title= {A Comparative Study of Unit Root Tests with Panel Data and A New Simple Test},
year = {1999},
doi = {10.1111/1468-0084.0610s1631},
journal = {Oxford Bulletin of Economics and Statistics },
volume = {61},
number = {S1},
pages = {631--652},
}