Liabsuetrakul, T. “Dilemma of “Randomized Controlled Trial” and ‘Observational Study’ in conducting health research”. Thai Journal of Obstetrics and Gynaecology, vol. 19, no. 1, Apr. 2017, pp. 1-3, https://he02.tci-thaijo.org/index.php/tjog/article/view/82176.