International Union of Official Travel Organisations. (1971). Methodology for annual and medium-term forecasts. International Union of Official Travel Organisations.
Chicago-referens (17:e uppl.)International Union of Official Travel Organisations. Methodology for Annual and Medium-term Forecasts. Geneva: International Union of Official Travel Organisations, 1971.
MLA-referens (9:e uppl.)International Union of Official Travel Organisations. Methodology for Annual and Medium-term Forecasts. International Union of Official Travel Organisations, 1971.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.