1. Helmer, O., Helmer-Hirschberg, O.: Looking forward: a guide to futures research. Sage Publications (1983)
2. Linstone, H.A., Turoff, M.: The Delphi method: techniques and applications. Addison-Wesley Pub. Co., Advanced Book Program (1975)
3. Dalkey, N.C., Corporation, R.: Delphi: Rand (1967)
4. Yousuf, M.I.: Using Experts’ Opinions through Delphi Technique. Practical Assessment Research & Evaluation 12 (2007)
5. Pfeiffer, J.: New look at education: systems analysis in our schools and colleges. Odyssey Press (1968)