Sarmento, Elsa de Morais, and Alcina Nunes. “The Evolution of the Sectoral Concentration in Portugal Between 1995 and 2006: The Herfindahl-Hirschman Index Perspective”. Tourism & Management Studies, vol. 11, no. 2, Jan. 2024, pp. 146-58, https://www.tmstudies.net/index.php/ectms/article/view/823.