Manual on Statistics of International Trade in Services

Population censuses and household surveys 
25. Statistics from population censuses are of limited 
usefulness for obtaining information relevant to mode 4 
because they are produced at long intervals and the 
results are available too late to help monitoring the 
current or recent developments with respect to the 
presence of foreign workers, in particular those present 
(or absent) only for a limited period. In addition, both 
the population census and household surveys are 
frequently limited to the resident population, and 
therefore do not cover short-term visitors involved in 
trade in services.