Taupikurrahman, Taupikurrahman, et al. “The International Tourism Demand for Indonesia: Expenditure Approach”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 48, no. 6, Nov. 2019, pp. 119-27, https://gssrr.org/JournalOfBasicAndApplied/article/view/10507.