4.67. Domestic tourism expenditure needs to be observed directly from the resident population by use of computer‑assisted telephone interviews (CATI) or other forms of household surveys. These can be designed either as specific operations or as a module of a larger household expenditure survey. The statistical challenges in designing household surveys has been discussed in chapter III (see sects. D.1 and D.2). Most issues covered in the previous section B.3 directly above, are also relevant here.
4.68. Because a (sometimes large) proportion of the sampled households will not include a member who engaged in some form of tourism activity in the reference period, a large number of households must be selected to ensure that there is a net sample providing sufficient information. Since the interviews are conducted after visitors return to their usual environment, leaving the hurry and pressure of travel behind, they may be able to recall their expenditures more easily and more precisely by reviewing bills, invoices and credit‑card receipts (particularly if they receive a letter informing them of the interview in advance). In support of this exercise, it is recommended that visitors be asked to describe their trips, including the different places visited and the activities engaged in, so that expenditures can be connected more easily with each of these components and their addition can thereby yield a figure for total expenditure.
4.69. An additional issue associated with domestic tourism expenditure, as compared with inbound tourism expenditure, is the fact that in many countries, visits of residents to vacation homes are frequent and thus frequently reported. Actual expenditure related to vacation homes and timeshares in the country of residence tends to fall into two broad categories:
a. Expenses related to ownership of the vacation home or timeshare that are more or less independent of any specific trip. Public utilities and maintenance fees fall in this category and might be reported in a different part of the expenditure survey. They should not be included in tourism expenditure (IRTS 2008, para. 4.7);
b. Expenses clearly associated with a specific trip to the vacation home, such as transportation and food. They should be reported within the specific tourism expenditure module.
4.70. As noted earlier, domestic tourism expenditure includes expenditure by visitors within their economy of origin for and on outbound trips. Such expenses are principally related to international transportation, reservation services paid to domestic travel agencies, services provided by residents, and any tourism expenses incurred during the leg of the trip that occurs in the country of residence (see paras. 4.19-4.20). It is important to collect information on such outbound trip expenditures that occur before departure from the country of residence. This information, which is not necessarily covered by domestic travel surveys, can also be derived from surveys on outbound trips.
4.71. So that more details may be obtained on certain aspects of visitor spending, subsamples of the selected population can be established according to a more detailed breakdown of expenditure. Such an approach has the advantage of allowing each respondent to provide the details relating to some but not necessarily all categories of expenditure, thereby making the interview procedure less burdensome while still permitting detailed information to be obtained. This approach assumes, however, that the size of the overall sample is sufficiently large to permit subsampling while still yielding reasonably precise information and allowing for the cross‑classification of observed variables (non‑monetary as well as monetary). As a result, the statistical design and grossing up procedures could be complex.
 It should be noted that, unlike the purchase of an imported good within the country of the outbound tourist, an imported service (which most often relates to transportation) is not part of tourism expenditure and hence should be excluded.