754. The recommendations and conventions set out in this chapter have been prepared with a view to ensuring that the census allocates each person to one, and only one, place of usual residence. This is important in an international context to avoid persons either being counted in the populations of more than one country or not being counted at all. The same principle applies within a national context. The following paragraphs provide definitions that should be applied in the context of census operations.

755. Enumeration means the act of collecting data about a person (or household), irrespective of whether this occurs with the direct participation of that person (or household) through a field operation, or indirectly using data already recorded in administrative sources or population registers.

756. Population is any set of persons attributed to a geographic entity who meet defined criteria at a specified reference time; these criteria should help to identify the qualifying characteristics that clarify which particular population is being referred to (such as the usually resident population or the working population).

757. To meet national requirements, a country may have an interest in various “populations”. To facilitate clarity in international comparisons, it is recommended that the descriptions of these populations (in terms of qualifying characteristics, and their associated adjectives and labels) make use of terminology and meanings that are as close as possible to the meanings used in the international context.

758. A country may wish to enumerate all persons present in their territory and/or supposedly belonging to the population of interest. The population to be enumerated is the set of persons whom the country decides should be covered by the census, regardless of their subsequent exclusion from any specific population count, as defined below. The enumerated population base is composed of those persons who have actually been enumerated. This may or may not equate to the target population (the population to be enumerated); that is, the coverage of the census may represent either an under-count or an over-count.

759. The population base is the population used for the compilation of statistical aggregates in a particular tabulation. This may be a sub-set, or the whole, of the population to be enumerated. A country may adopt more than one population base (for different statistical purposes), but one of these should always be the population base used for international comparison purposes (most often the “usually resident” population).

760. For particular statistical needs, countries may wish to adopt an additional or supplementary⁶⁹ population base – such as the daytime or workplace population. This should be seen as an addition to the population bases used for international comparison purposes, and not an alternative.

761. A population count is the aggregate obtained by the simple addition of individual records from the enumerated population base. A “population estimate” is the aggregate obtained as the outcome of a statistical method of estimation. Therefore, both the population count and the population estimate refer to a specific population base and are empirical measures.

762. The census reference time is the time to which any information collected in a census refers. It can be either a precise moment of a day, usually midnight (“census reference moment”), or a period of time (“census reference period”), or a day selected as indicative of a period (“census reference average day”). Some topics will refer to a particular moment (providing stock data), others to a period (flow data), and usually the census reference period includes the census reference time. The “census day/period” is the day/period in which a census is carried out. There is a risk that this will be confused with the census reference time, and countries should guard against this in the internal and external documentation of the census.

763. The place of usual residence is the place where the enumerated person usually spends their daily rest, assessed over a defined period including the census reference time.

764. The population base to be used for international comparison purposes is the usually resident population. The usually resident population of a country is composed of those persons who have their place of usual residence in the country at the census reference time and have lived, or intend to live, there for a continuous period of at least 12 months. A “continuous period” means that absences (from the country of usual residence) whose durations are shorter than 12 months do not affect the country of usual residence. The same criteria apply for any relevant territorial division (being the place of usual residence) within the country.

765. If a country cannot adopt the usually resident population as its population base (or as one of its population bases), it should put all possible efforts into producing estimates that are as close as possible to the usually resident population using its own population base(s).

766. As part of the estimation process in register-based censuses, whenever reference is made to actual geographic places for the usually resident population base, it could be replaced by the registered place of residence. In practice, an increasing number of register-based countries apply additional estimation methods often denoted as “signs of life”. These methods typically link various administrative or other auxiliary data sources to obtain an indication of actual presence of persons in the place where they are registered. International guidelines mention signs-of-life methods as a good practice.⁷⁰

767. On the basis of the definition of the place of usual residence, persons usually resident in the place of enumeration but absent, or expected to be absent, at the census reference time for less than one year should be considered as “temporarily absent persons” and thus included in the total population.

768. The group of absent persons living abroad (former members of a household who now live or are expected to live in another country) for one year or more can be particularly important in countries experiencing high levels of emigration. Some countries try to estimate emigration in the census by collecting data on these persons, for instance using an emigration module in the questionnaire. Previous experiences⁷¹ have shown that the census is unlikely to provide an accurate count of the total number of emigrants residing abroad. However, such an approach may provide some information on sub-sets of emigrants, such as those who emigrated recently and those who have close family ties in the country.

769. If data on absent persons living abroad for one year or more are to be collected through the census, their information (in terms of numbers and characteristics) should be distinguished clearly from the information collected for the usually resident population. Every effort should be made to avoid absent persons living abroad from being included in the usually resident population. This may include, for example, listing absent persons living abroad on a separate section of any census enumeration form, with clear instructions to both respondents and enumerators.

770. A total usually resident population count for each territorial division would normally be compiled by adding persons who are usually resident and present to those who are usually resident but temporarily absent. However, it is not always possible to collect information about persons absent from their place of usual residence, particularly if a whole household is temporarily absent at the census reference time. Provision must therefore be made to collect information about such persons at the place where they are found at the census reference time, and if necessary “transfer” them to their place or territorial division of usual residence, using the information recorded about their place of residence. This may be done, for example, by including in the census enumeration all persons and households present on the census day, and assigning them to their correct place of usual residence using the information collected. Alternatively, or in parallel, a follow-up visit by enumerators to apparently occupied dwellings where there was previously no contact with residents may allow information to be collected on persons and households who are usually resident at that census reference time but were temporarily absent on census day. Care must be taken in such processes to avoid double enumeration whereby a person or household is incorrectly recorded as usually resident at more than one address.

771. Each country should compile a figure for the total usually resident population, and the detailed tabulations should in general be provided on this basis. In those countries where the total population figure has been adjusted for under- or over-enumeration (usually measured by use of a post-enumeration survey or by comparison with other sources), both the enumerated figure (the population count) and the adjusted population figure (the population estimate) should be shown and described. However, national legislation may prevent this or, conversely, make it an obligation. The detailed tabulations may, however, be based only on the population that was actually enumerated.

772. The composition of the usually resident population should be described in detail in the census report(s). As far as is possible given the census data sources and methodologies adopted by a country, the total usually resident population should include all persons who have their usual residence in the country or relevant territorial division, regardless of their legal status.

773. There are various population groups for which some uncertainty may arise about their inclusion in the usually resident population of a country. The following persons should be included:

(a) Persons present at the census reference time to whom the concept of usual residence does not apply (such as nomads and vagrants), irrespective of whether or not they meet the 12-month criterion;

(b) Persons who regularly live in more than one country during a year, if the reporting country is the one where they live most of the time, irrespective of whether or not they are present in the reporting country at the reference time;

(c) National military, naval and diplomatic personnel and their families, located outside the country, irrespective of their duration of stay abroad;

(d) Foreign persons working within the country for international businesses or organizations (but not including foreign diplomats or military forces) and their families, provided that they meet the criteria for the usual residence in the country;

(e) Seafarers and people working on fishing boats usually resident in the country but at sea at the census reference time (including those who have no place of residence other than their quarters aboard ship);

(f) Irregular or undocumented migrants, who are foreigners and who are staying in a country without the appropriate documentation, provided that they meet the criteria for the usual residence in the country;

(g) Asylum seekers and persons who have applied for, or been granted, refugee status or similar types of international protections, regardless of the type of accommodation they live in, providing they meet the criteria for usual residence in the country;

(h) Children born in the twelve months before the census reference time and who, at the census reference time, are expected to be resident in the country for 12 months or more based on the intention of the household members that they live with.

774. For (f) and (g) above, the intention is not to distinguish these persons separately, but rather to ensure that they are not missed from the enumeration. This includes the children of people falling under categories (f) and (g), as well as unaccompanied and separated children⁷² living in institutional household (e.g., in residential alternative care facilities) or private households (e.g., in foster families).

775. The following persons should instead be excluded from the usually resident population of a country:

(a) Persons who regularly live in more than one country during a year, if the reporting country is NOT the one where they live most of the time, irrespective of whether or not they are present in the reporting country at the census reference time; and

(b) Foreign military, naval and diplomatic personnel and their families, located in the country, regardless of their duration of stay.

776. For persons who, at the census reference time, have spent, or are likely to spend, twelve months or more living in a communal establishment or institution, the institution should be taken as the place of usual residence. Examples of persons living in institutions include patients in hospices or long-stay hospitals, persons in nursing homes or convalescent homes, children in residential alternative care facilities, prisoners and those in juvenile detention centres.

777. The examples in paragraphs ‎773–‎775 above are provided for guidance, primarily for countries conducting a field data collection for the census. It is recognized that determining whether members of certain population groups should be included in or excluded from the usually resident population can be challenging, particularly for countries using registers.

778. It may be particularly problematic to determine the country of usual residence or the place of usual residence within the country for persons who work or study away from home.

779. The principal home may be defined as an address that a person has an established link with, even if this is not their current place of usual residence as defined in paragraph ‎763. This is particularly relevant for persons who study or work away from home. The established link with the principal home may be on the basis of one or more factors, such as past and intended future usual residence at that address, or the ongoing usual residence at that address of members of the person’s family nucleus.

780. Table 3 summarizes the recommended guidelines of classification for students and workers who live away from the principal home for 12 months or more. For the sake of conformity with the global Principles and Recommendations for Population and Housing Censuses – Revision 4 issued by UNSD, students in tertiary education should be allocated to their term-time address, when studying within the country. When studying abroad they should not be included in the population of the country of their principal home, since their place of usual residence should be the term-time address in the country where they study, even if they regularly return to the principal home. However, it is acknowledged that in some countries there may be considerations (such as higher coverage during field enumeration, or a particularly large number of emigrating students) that would justify the allocation of these students to their principal home.

781. There are other population groups for which some uncertainty may arise in defining their place of usual residence within the country. The recommended conventional treatment of these cases is as follows:

(a) For persons without a usual residence, such as homeless or roofless persons, nomads, itinerant migrants and workers, the place of usual residence should be the place of enumeration;

(b) When a person regularly lives in more than one residence within the country during the year, the place of usual residence should be the place where the person spends most of their time, or their registered place of residence, irrespective of whether or not the person is present in that place at the census reference time;

(c) A child who alternates between two households within the country (for instance following their parents’ separation or divorce) should consider the household where they spend the majority of the time, or their registered place of residence, as their place of usual residence. Where an equal amount of time is spent with both parents, the place of usual residence should be the same as that of the parent or household with whom the child is living at the census reference time.

782. For the national military, naval and diplomatic service personnel and their families located outside the country the following classification rules should be applied:

(a) If they are residing abroad for less than 12 months and they are intending to return to the place of departure, they should be allocated within the country in accordance with the rules for usual residence. In particular, they could be allocated to (by decreasing order of priority):

(b) The principal home address within the country, if any; or the duty station within the country to which they were attached before leaving;

(c) If they are residing abroad for at least 12 months or if they are not intending to return to the place of departure (although returning to the country within a 12-month period), they should be attributed to a “virtual place” (extra-region) of the country of departure.

Notes:

* “Regular” is taken to mean more than twice each month.

** See paragraph ‎979 for the definition of family nucleus.

*** ISCED 2011 levels 0–4.

**** ISCED 2011 levels 5–8.

^ Term-time address is the address at which a schoolchild or student lives while attending their studies. This may or may not be the same as their principal address.