1. Robert F. Nelson, 11th International Telecommunications Energy Conference (INTELEC 89), I.E.E.E., 1989.
2. J.F. Lawless, Statistical Models and Methods For Lifetime Data, Wiley, New York, 1982.
3. R.G.D. Steel, J.H. Torrie, Principles and Procedures of Statistics: A Biometrical Approach, McGraw-Hill, New York, 1980, pp. 535–537.