บุญวัฒนะกุล ช. “A Synthesis of Graduate Students Research in Non-formal and Informal Education, School of Educational Studies, Sukhothai Thammathirat Open University”. STOU Education Journal, vol. 10, no. 2, May 2018, pp. 152-63, https://so05.tci-thaijo.org/index.php/edjour_stou/article/view/128795.