Boonsit, P., W. Kijtorntham, and N. Supparerkchaisakul. “Development of Personal Growth Initiatives, Self-Leadership and Self-Directed Learning in English Among of Thai Undergraduate Students for the Free Flow of Skilled Labor in the ASEAN Community”. Journal of Behavioral Science for Development, vol. 12, no. 2, July 2020, pp. 45-62, https://so02.tci-thaijo.org/index.php/JBSD/article/view/239950.