Sudjai, Narumol, and Monthira Duangsaphon. 2020. “The Bias Reduction in Observational and Quasi-Experimental Studies by Using Propensity Score Method”. Journal of Science Ladkrabang 29 (2):86-100. https://li01.tci-thaijo.org/index.php/science_kmitl/article/view/241248.