Malawal Phattarapong, Wongchai Anupong, and Lin Yi-Chia. “Cost Efficiency of Rubber Farmers in the Upper Northern Provinces of Thailand”. International Journal of Advanced Science and Technology 29, no. 9s (May 19, 2020): 4411 - 4418. Accessed May 8, 2024. http://sersc.org/journals/index.php/IJAST/article/view/16917.