1. Bartholomew, D.J., Forbes, A.F., McClean, S.I., 1991. Stastistical Techniques for Manpower Planning, 2nd ed. Wiley, New York
2. Bartholomew, D.J., 1982. Stochastic Models for Social Processes, 3rd ed. Wiley, New York
3. Cascio, W.F., 1987. Costing Human Resources. Kent Publishing
4. Patterns of growth and specialization in executive search industry;Feldman;Journal of Managerial Issues,1997
5. It's costing to lose good employees;Fitz-Enz;Workforce,1977