Pongpullponsak, Adisak, Wichai Suracherkeiti, and Chaowalit Panthong. 2015. “The Economic Model of X̄ Control Chart Using Shewhart Method for Skewed Distributions”. Thailand Statistician 7 (1):81-99. https://ph02.tci-thaijo.org/index.php/thaistat/article/view/34324.