Suwanakul, Sontachai, and Eric J. Wailes. 1987. “Estimates of Structural Relationships for the World’s Rubber Market with Particular Emphasis on Thailand’s Natural Rubber Industry”. Kasetsart Journal of Social Sciences 8 (2):173-88. https://so04.tci-thaijo.org/index.php/kjss/article/view/243841.