5Penrose,Edith.The Theory of the Growth Of the Firm [M].New York, NY:Willey,1959.
6Meador, J. W., H. E. Ryan, Jr, and C. D. Schellhorn, Product Focus Versus Diversification: Estimates of X -Efficiency for the US Life Insurance Industry, in: P. T.Harker and S.A.Zenios, eds.,Performance of Finan- cial Institutions: Efficiency, Innovation, Regulation [M].New York : Cambridge University Press, 2000.
