6Levin, A., C. Lin and C. Chu. Unit Root Tests in Panel Data: Asymptotic and Finite-Sample Properties [J ]. Journal of Econometrics, 2002, 108:1-24.
7Breitung, Jorg. The Local Power of Some Unit Root Tests for Panel Data, in B. Baltagi (ed).Advances in Econometrics, Vol, 15: Nonstationary Panels, Panel Cointegration, and Dynamic Panels, Amsterdam:JAl Press, 2000, 161 - 178.
8Hardi, Kaddour. Tesing for Stationariry in Heterogeneous Panel Data [J], Econometric Joumal, 2003,3: 148-161.
9Im, K.S., Pesaran, M.H., and Shin, Y.. Testing for Unit Roots in Heterogeneous Panels [J]. Journal of Econometrics, 2003,115:53-74.
10Maddala G.S.,Wu Shaowen .A Comparative Study of Unit Rool Tests with Panel Data and a New Simple Test. Oxford Bulletin of Economics and Statistics, 1999,61:631-652.