Ribeiro, E. da C., and B. Wang. “Tourism Led Growth Hypothesis: Has the Tourism Industry an Impact on The Economic Growth of Sao Tome and Principe?”. International Journal of Economics and Financial Issues, vol. 10, no. 1, Dec. 2019, pp. 180-5, https://www.econjournals.com/index.php/ijefi/article/view/9105.