The compilation and publication of statistics on tourism and travel is the responsibility of the Central Statistics Office (CSO). Such statistics are compiled on the basis of two sample surveys of passengers, the country of residence survey and the passenger card inquiry, which are carried out by the CSO using internationally accepted definitions and methodologies, in conjunction with actual figures for total passenger movements, supplied by the air and sea carriers.
I am advised by the CSO that they are satisfied that their survey methods and the resultant statistics provide an accurate measurement of overseas visitor numbers and their expenditure from year to year, although it keeps the system subject to continual review and refinement.