| Census Characteristics | 1981 | 1991 | 2001 |
| Title | XII Population Census and II Household Census | XIII Population Census and III Household Census | XIV Population Census and IV Household Census |
| Census Agency | Portugal Instituto Nacional de Estatistica(INE) | Portugal Instituto Nacional de Estatistica (INE) | Portugal Instituto Nacional de Estatistica (INE) |
| Population | 9.833.014 | 9.867.147 | 10.356.117 |
| Universe | 100% | 100% | 100% |
| De jure or de facto | De jure | De jure | De jure |
| Enumeration unit | Dwelling | Dwelling | Dwelling |
| Census day | 16 March 1981 | 15 April 1991 | 12 March 2001 |
| Field work period | February - June | March - July | February - June |
| Enumeration forms used | One questionnaire for each of the following statistical units: building, housing unit, household, individual, and "collective questionnaire" (for groups of individuals presents but not residents). | One questionnaire for each of the following statistical units: building, housing unit, private household, institutional household, individual and "collective questionnaire" (for groups of individuals presents but not residents). | One questionnaire for each one of the following statistical units: building, housing unit, private household, institutional household, individual and "collective questionnaire" (for groups of individuals presents but not residents). |
| Type of field work | Direct enumeration | Direct enumeration | Direct enumeration |
| Respondent | Householder | Householder | Householder |
| Coverage | - | Buildings-99,60%; Dwellings- 99,42%;households-99,24%; individuals-99,04% | Buildings-99,7%; Dwellings- 99,5%;households-101,1%; individuals-100,7% |
| Microdata sample characteristics | 1981 | 1991 | 2001 |
| Sample microdata source | Portugal Instituto Nacional de Estatistica (INE) | Portugal Instituto Nacional de Estatistica (INE) | Portugal Instituto Nacional de Estatistica (INE) |
| Sample design | Systematic, for every 20th dwelling/housing unit, excluding collective dwellings, with the start on first dwelling of each one of the seven NUTS II. Persons living in the collective dwellings were selected apart but using the same methodological approach. | Systematic, for every 20th dwelling/housing unit, excluding collective dwellings, with the start on the first dwelling of each one of the seven NUTS II. Persons living in the collective dwellings were seleceted apart but using the same methodological approach. | Systematic, for every 20th dwelling/housing unit, excluding collective dwellings, with the start on the first dwelling of each one of the seven NUTS II. Persons living in the collective dwellings were selected apart but using the same methodological approach. |
| Sample unit | Dwelling for private dwellings; person for collective dwellings | Dwelling for private dwellings; person for collective dwellings | Dwelling |
| Sample fraction | 5 % | 5 % | 5 % |
| Sample fraction (private households) | - | - | - |
| Sample fraction (institutional households) | - | - | - |
| Sample size (person records) | 492.289 | 491.755 | 517.026 |
| Sample size (private households) | - | - | - |
| Sample size (institutional households) | - | - | - |
| Sample weights | Self-weighting (expansion factor=20) | Self-weighting (expansion factor=20) | Self-weighting (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 | Yes, if we consider unset | Yes, if we consider unset | Yes, if we consider unset |
| Special populations | No | No | No |
| Unit definitions | 1981 | 1991 | 2001 |
| Dwellings | Are structurally separate and independent and designed for permanent human habitation at a fixed location. They are not used wholly for other purposes at the time of the census or are actually used as the principal usual residence of at least one person at the time of the census | Are structurally separate and independent and designed for permanent human habitation at a fixed location. They are not used wholly for other pruposes at the time of the census or are actually used as the principal usual residence of at least one person at the time of the census. | Are structurally separate and independent and designed for permanent human habitation at a fixed location. They are not used wholly for other purposes at the time of the census or are actually used as the principal usual residence of at least one person at the time of the census. |
| Households | Group of persons living at the same dwelling and that have kinship relations among them ("de jure" or "de facto"), regardless of occupying the whole or part of the housing unit. A person who lives alone in a separate housing unit or who occupies, as a logder, a separate room (or rooms) of a housing unit, but does not have kinship relations with the other occupants | Group of persons living at the same dwelling and that have kinship relations among them ("de jure" or "de facto"), regardless of occupying the whole or part of the housing units. A person who lives alone in a separate housing unit or who occupies, as a logder, a separate room (or rooms) of a housing unit, but does not have kinship relations with the others occupants. | Group of persons living at the same dwelling and that have kinship relations among them ("de jure" or "de facto"), regardless of occupying the whole or part of the housing unit. A person who lives alone in a separate housing unit, or who occupies, as a logder, a separeate room (or rooms) of a housing unit, but does not have kinship relations with the other occupants. |
| Institutional population | Group of persons living in a collective housing unit (institution) that, regardless of the family relationship among them, they respect common rules, are beneficiaries of the purposes of the institution, and are ruled by a specific entity within or without that group | Group of persons living in a collective housing unit (institutional) that, regardless of the family relationship among them, they respect common rules, are beneficiaries of the purposes of the institution, and are ruled bu a specific entity within or without that group. | Group of persons living in a collective housing unit (institution) that, regardless of the family relationship among them, they respect common rules, are beneficiaries of the purposes of the institution, and are ruled by a specific entity within or without that group. |
| Group quarters | Group of persons living in a collective housing unit (institution) that, regardless of the family relationship among them, they respect common rules, are beneficiaries of the purposes of the institution, and are ruled by a specific entity within or without that group | Group of persons living in a collective housing unit (institutional) that, regardless of the family relationship among them, they respect common rules, are beneficiaries of the purposes of the institution, and are ruled bu a specific entity within or without that group. | Group of persons living in a collective housing unit (institution) that, regardless of the family relationship among them, they respect common rules, are beneficiaries of the purposes of the institution, and are ruled by a specific entity within or without that group. |
| Unsettled population | Not available | Not available | Not available |
in collaboration with Minnesota Population Center 
