- Valk, W. van der, Sumo, R., Dul, J. & Schroeder, R. (2016). When are contracts and trust necessary for innovation in buyer-supplier relationships? A Necessary Condition Analysis. Journal of Purchasing and Supply Management, 22(4), 266-277.*
- Valk, W. van der, Sumo, R., & Dul, J. (2014). How contracts and trust influence innovation in inter-organizational relationships: A necessary condition analysis. In: Editors: H. Badenhorst, et al. 23rd International Purchasing and Supply Education and Research Association Conference (IPSERA 2014), Pretoria, South Africa, 13-16 April 2014 (pp 1-20).
- Valk, W. van der, & Wynstra, F. (2012). Buyer-supplier interaction in business-to-business services: A typology test using case research. Journal of Purchasing and Supply Management, 18(3), 137-147.
