Le tourisme au Portugal [Estatísticas de 1964 a 1968.] : problemes de planification / Roland Olivier
Património cultural em Portugal: : Avaliação do valor económico e social / Catarina Valença Gonçalves [et al.]
Economic concepts relevant to the study of outdoor recreation / E. Boyd Wennergren, Warren E. Johnston
Comparison of methods for recreation evaluation / Jack L. Knetsch, Robert K. Davis