Silitonga, Roland Y.H., Senator Nur Bahagia, Tota Simatupang, and Joko Siswanto. 2013. “Modeling the Competitiveness of Indonesian Palm Oil Industry: A Conceptual Model Using Hierarchical Multi-Level System Approach”. Jurnal Teknik Industri: Jurnal Keilmuan Dan Aplikasi Teknik Industri 15 (2):103-10. https://doi.org/10.9744/jti.15.2.103-110.