| Census Characteristics | 1981 | 1991 | 2001 |
| Title | Census of Population and Housing 1981, Spain | Census of Population and Housing 1991, Spain | Census of Population and Housing 2001, Spain |
| Census Agency | Instituto Nacional de Estadisticas (INE) | Instituto Nacional de Estadisticas (INE) | Instituto Nacional de Estadisticas (INE) |
| Population | The census includes persons who have a fixed residence in the national territory as well as those who are in the national territory at the time of reference, without omissions nor duplications.The persons who have their residency in Spain constitute the fixed population [population with rights]. The persons who are in the national territory at the moment of the census form the actual population [de facto]. | The census includes persons who have a fixed residence in the national territory as well as those who are in the national territory at the time of reference, without omissions nor duplications.The persons who have their residency in Spain constitute the fixed population [population with rights]. The persons who are in the national territory at the moment of the census form the actual population [de facto]. | Residents: persons who at the time of the census habitually reside in Spain. This excludes those persons who were in Spain at the time of the census, but did not reside there. The only exception are citizens and residents temporarily abroad. |
| Universe | | | |
| De jure or de facto | De facto | De facto | De facto |
| Enumeration unit | | | |
| Census day | 1 March 1981 | 1 March 1991 | 1 November 2001 |
| Field work period | - | 1 March-1 April 1991 | Approcimatelly two months |
| Enumeration forms used | Two types of questionnaires will be used: one for the population that lives in family dwellings and another for the population that lives in collective dwellings. | There are five forms: general questionnaire, individual questionnaire, collective [dwelling] questionnaire, secondary dwellings with no registered dwellers, and 1990 building questionnaire. | The are four forms: the dwelling, censal data, household data, and individual data forms. |
| Type of field work | The questionnaires are prepared to utilize the method of self-enumeration, with which the mission of the Agent is reduced, generally, to the tasks of delivering and collecting the questionnaires and verifying the correct completion of the same. | The questionnaires are prepared to utilize the method of self-enumeration, with which the mission of the Agent is reduced, generally, to the tasks of delivering and collecting the questionnaires and verifying the correct completion of the same. | The enumerator is the main form of data collection. However, data can be provided by telephone or internet. The forms are designed to allow the respondents to fill them without any help. |
| Respondent | | | |
| Coverage | | | |
| Microdata sample characteristics | 1981 | 1991 | 2001 |
| Sample microdata source | Integrated European Census Microdata | Integrated European Census Microdata | Integrated European Census Microdata |
| Sample design | Systematic stratified sampling. The provinces of Alava, Guipuzcoa, Navarra, and Vizcaya were over-sampled at roughly 5 times the rate of other provinces. | Systematic stratified sampling | Systematic stratified sampling |
| Sample unit | Dwelling | Dwelling | Dwelling |
| Sample fraction | 5% | 5% | 5% |
| Sample fraction (private households) | | | |
| Sample fraction (institutional households) | | | |
| Sample size (person records) | 2.084.221 | 1.931.458 | 2.039.274 |
| Sample size (private households) | | | |
| Sample size (institutional households) | | | |
| Sample weights | Computed by census agency. Use of weights is strongly recommended because of oversampling of several | Computed by census agency and should be used for most types of analysis | Expansion factor = 20. |
| Units identified | 1981 | 1991 | 2001 |
| Dwellings | Yes | Yes | Yes |
| Vacant units | Yes | Yes | Yes |
| Households | Yes | Yes | Yes |
| Individuals | Yes | Yes | Yes |
| Group quarters | Yes | Yes | Yes |
| Settled/unsettled Population | - | - | - |
| Special populations | - | - | - |
| Unit definitions | 1981 | 1991 | 2001 |
| Dwellings | A dwelling is a structurally separate and independent location that, given the way it was built, rebuilt, transformed, or adapted, is conceived to be inhabited by persons, or, even if this is not the case, is effectively and actually inhabited at the time | A dwelling is a structurally separate and independent location that, given the way it was built, rebuilt, transformed, or adapted, is conceived to be inhabited by persons, or, even if this is not the case, is effectively and actually inhabited at the time of the census. | A dwelling is a structurally separate and independent location that, given the way it was built, rebuilt, transformed, or adapted, is conceived to be inhabited by persons, or, even if this is not the case, is effectively and actually inhabited at the time of the census. |
| Households | Group of persons, generally linked because they are relatives, who live together, normally occupying the totality of a dwelling. Persons in domestic services who spend the night in the dwelling and guests who are part of the family group will be included as family. | Group of people who, residing in the same dwelling, share expenses derived from the use of the dwelling and/or alimentation. Single person and multiperson households are to be considered. | Group of people residing in the same family dwelling. Sharing of expenses is not required. Family dwellings are those inhabited by one or more persons usually, but not necessarily, having kindred ties and who do not constitute a group quartes [see definition below]. |
| Institutional population | - | - | - |
| Group quarters | Collective dwellings are those dwellings or buildings designed to be occupied by persons who do not constitute a family, subject to a common regime or authority, or gathered by common objectives or interests. | Collective dwellings are those dwellings or buildings designed to be occupied by persons who do not constitute a family, subject to a common regime or authority, or gathered by common objectives or interests. | Collective dwellings are those dwellings or buildings designed to be occupied by persons who do not constitute a family, subject to a common regime or authority, or gathered by common objectives or interests. |
| Unsettled population | - | - | - |
in collaboration with Minnesota Population Center 
