กีรติวิบูลย์ ว. “Comparisons of Opinions between Students Unwithdrawn and Withdrawn Calculus 1 of Thaksin University”. KKU Science Journal, vol. 44, no. 1, Mar. 2016, pp. 222-36, https://ph01.tci-thaijo.org/index.php/KKUSciJ/article/view/249492.