1. G, Altschuller, L, Shulyak, S, Rodman, (2002). 40 Principles: TRIZ Keys to innovation (Vol. 1). Technical Innovation Center, Inc. Worcester, M.A. U.S.A.
2. H, Banwell, (1964). The Placing and Management of Contracts for Building and Civil Engineering Work: The Banwell Report. Available at: https://onlinelibrary.wiley.com/doi/10.1002/9780470758526.ch5. Accessed: 03/09/2021.
3. D, Bodnar, (2021). Brexit and COVID-19 Challenges Disrupt UK-EU Trade. Available at: https://www.sdcexec.com/sourcing-procurement/article/21590762/atradius-brexit-and-covid19-challenges-disrupt-ukeu-trade. Accessed: 24/08/2021.
4. Correlation and regression: applications for industrial organizational psychology and management;Bobko,2001
5. Social research methods;Bryman,2016