Chaikipinyo, S., S. Soontrapa, and C. Mahakkanukrauh. “Normative Reference Grading Program”. Srinagarind Medical Journal, vol. 4, no. 3, Nov. 2013, pp. 218-27, https://li01.tci-thaijo.org/index.php/SRIMEDJ/article/view/13505.