Census advisory
The United Nations recommends a census enumeration at least once every ten years, and once every five years for even better data, rather than simply relying on estimates and projections alone. Complications to carrying out a census include tribal conflict, war, borders not demarcated, budget, inexperience, political snags, lack of manpower, and poor geographic information systems. A number of nations have not carried them out once a decade. It is not uncommon for a scheduled census to be deferred or delayed
Lebanon has not held a census since 1932. Afghanistan is closing in on four decades without a census DRC and Uzbekistan stand out as not having a census since before 1990 Madagascar has not had counts since the 1990s. Eritrea has only had one as a part of Ethiopia in the 90s
More countries are switching to using administrative data to hold a census. This allows a simulated census to be conducted by linking several different administrative databases at an agreed time