Sombutboon, J., N. Prakas, and B. Eiu-Seeyok. “Happiness of Thai Elderly in Thailand 4.0”. Journal of Phrapokklao Nursing College, Chanthaburi, vol. 30, no. 2, June 2019, pp. 219-28, https://he01.tci-thaijo.org/index.php/pnc/article/view/199567.