C. J. Gelderman and A. J. Van-weele, Handling measurement issues and strategic directions in Kraljic's purchasing portfolio model, Journal of Purchasing and Supply Management, vol.9, issue.5-6, pp.5-6, 2003.
DOI : 10.1016/j.pursup.2003.07.001

C. J. Gelderman and A. J. Van-weele, Purchasing Portfolio Models: A Critique and Update . The Journal of Supply Chain Management, 2005.
DOI : 10.1111/j.1055-6001.2005.04103003.x

URL : http://repository.tue.nl/622404

C. J. Gelderman and J. Semeijn, Managing the global supply base through purchasing portfolio management, Journal of Purchasing and Supply Management, vol.12, issue.4, pp.209-217, 2006.
DOI : 10.1016/j.pursup.2006.10.002

P. Kraljic, Purchasing Must Become Supply Management, Harvard Business Review, vol.615, pp.109-117, 1983.

C. Okoli and S. D. Pawlowski, The Delphi method as a research tool: an example, design considerations and applications, Information & Management, vol.42, issue.1, pp.15-29, 2004.
DOI : 10.1016/j.im.2003.11.002

R. F. Olsen and L. M. Ellram, A Portfolio Approach to Supplier Relationships. Industrial Marketing Management, pp.101-113, 1997.

R. R. Yager, On Ordered Weighted Averaging Aggregation Operators in Multi-criteria Decisions, IEEE Trans. on Systems, Man, and Cybernetics, vol.81, pp.183-190, 1988.

H. J. Zimmermann, Fuzzy Sets, Decision Making, and Expert Systems, International Series in Management Science and Operations Research, 1993.
DOI : 10.1007/978-94-009-3249-4