7James J Heckman, 1979, " Sample Selection Bias as a Specification Error", Econometrica, Vol. 47 No. 1 ( Jan. ).
8Stiglitz, Joseph, Andrew Weiss, 1981, "Credit Rationing in Markets with Imperfect Competition'", American Economic Review 71(3) : 393 -410.
9Tsai, Kelly , 1999, Financing Private Enterprises in China : A Political Economic View from Below, paper presented at the 1999 Association for Asian Studies annual meeting, Boston.
10Villas-Boas J, and U Schmidt-Mohr , 1999 , Oligopoly with Asymmetric Information: Differentiation in Credit Markets, The RAND Journal of Economics 30 ( 3 ) : 375 - 396.