Kittilertpaisan, Jitti, Kallaya Kittilertpaisan, and Phakhaphon Khatiwat. 2016. “Technical Efficiency of Rubber Farmers’ in Changwat Sakon Nakhon: Stochastic Frontier Analysis”. International Journal of Economics and Financial Issues 6 (6S):138-41. https://econjournals.com/index.php/ijefi/article/view/3144.