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Methodology

Methodology

CSO statistical publication, , 11am
Frontier Series Output

CSO Frontier Series outputs may use new methods which are under development and/or data sources which may be incomplete, for example new administrative data sources. Particular care must be taken when interpreting the statistics in this release.
Learn more about CSO Frontier Series outputs.

Methodology

This Frontier Series Release aims to estimate the number of Family and Household units in April 2022 using administrative data. 

The usually resident population is as defined in the IPEADS 2022 methodology. Based on attributes of this population gathered from administrative data sources, family and household estimates are generated.

In this methodology chapter, a detailed description of proposed family and household estimates are described, along with a description of the challenges faced by these methods in generating these estimates from administrative data. All methods use pseudonymised data only, to preserve privacy.

The methodologies described in this release are under development. Therefore, this release is categorised as a CSO Frontier Series Output. Care must be taken when interpreting the statistics in this release.

Family Estimates Methodology

In this release, a family is defined as a married couple (with or without children), cohabiting couple (with or without children) or a one parent family. Family members must be usual residents of the relevant household. The steps below detail how these families are counted in administrative data. 

Identifying Families

The Central Records System (CRS) from the Department of Social Protection relationship dataset is used to create a method to link individuals based on their family relationships, such as parents, partners, and children.

The process begins by selecting each unique individual by a unique pseudonymised Protected Identifier Key (PIK) and extracting all associated relationships, including children, parents, and partners. These are then used to create a matrix of family relationships in the administrative population.

This matrix excludes individuals who do not meet the definition of a family, such as single individuals without children, who are not, in turn, classified as children in another family.

Each identified family is assigned a unique pseudonymised Protected Identifier Key called the Family Unit PIK.

Since the Irish Family and Household Estimates methodology currently does not consider multigenerational family structures, adjustments are made to prevent individuals incorrectly appearing in multiple roles. Individuals who are classified as parents or partners are reviewed to ensure that they are not also incorrectly listed as children in another family.

Assigning Familial Roles

To ensure consistency and comparability, a Family Nuclei Code (FNC) is assigned to define each individual's role within a family, structured around a selected Head of Family This Head of Family designation is chosen randomly as a technical measure to help organise the family data.

FNC Codes:

FNC 1: Identifies the Head of Family.

FNC 2: Assigned to the partner of the Head of Family (if applicable).

FNC 3: Designates children within the family. These include biological, step, and foster children under the care of the Head of Family and their partner.

Classifying Family Types

Families are grouped by their Family Unit PIK and they are then analysed to determine the roles of members and classified into family types:

One-Parent Families: Classified as either “Single Mother” or “Single Father” families based on the parent’s sex as recorded in administrative data. These are then aggregated into the broader category of “One Parent (Fathers and Mothers)”.

Two-Parent Families:

With children: Classified as “Married Couple with Children” or “Cohabiting Couple with Children.”

Without children: Classified as “Married Couple without Children” or “Cohabiting Couple without Children.”

These family types are then aggregated into the broader categories of “Married with/without Children” and “Cohabiting with/without Children”.

Addressing Gaps in Data

Adult Children:

Adult children (FNC 3) aged over 18 are evaluated to determine if they reside with their parents or live independently. The CSO uses pseudonymised Eircode data as described in the Introduction to the Household Estimates Methodology below.

If an adult child’s Eircode indicates a separate residence, they are reclassified as “Single with No Children” and removed from the family nucleus.

Challenges of the Family Methodology

1. Cohabiting Couples Without Children

Couples living together without children may be less likely to report their relationship status, as there is often no perceived administrative requirement to do so. This can create challenges in accurately representing these families in data.

2. One Parent Families

Differentiating between single mothers and single fathers requires careful consideration. Developments are ongoing to improve processes for identifying the primary caregiver in cases where parents are separated, ensuring the statistics reflect these arrangements accurately.

3. Couples with Children

For couples with children, understanding the dynamics of families with young adults (who are often highly mobile due to work or further education) requires particular attention to ensure accurate statistics.

Interpreting Family Estimates

The methodology described above is developmental and this release is categorised as a CSO Frontier Series Output. Care must be taken when interpreting the statistics in this release.

The below table compares the counts of family units in Irish Family and Household Estimates from Administrative Data Sources 2022 alongside an aggregation of the counts of family units from Census 2022. Care should be taken in making comparisons with Census due to differences in data sources and methodologies.

Table 1: Family units by type based on administrative data methodologies and Census of Population, 2022

Household Estimates Methodology

Introduction

In the Irish Population Estimates from Administrative Data Sources (IPEADS) release series, the key variable in adding geography to the population file is the Eircode Pseudonymised Identifier Key (PIK). When a person's record has an associated Eircode PIK, it is possible to produce statistics on that person at all levels of geography. Similarly to IPEADS, in this release the Eircode PIK remains key to the estimation of household and family statistics. In IPEADS 2022, the Eircode PIK was assigned by identifying the address with the latest administrative activity associated with the person. If that address had an associated Eircode PIK, it was assigned to the person. If no Eircode PIK was associated with the address, a matching exercise was conducted to establish if there was an Eircode PIK for that address on an alternative dataset.  

For this release, an extra step was added. In a case where no Eircode PIK was assigned to a person, an Eircode PIK from the 2022 Census of Population was added to a record where a match was possible.

Next, where no Eircode PIK was found, the CSO matched the address to an address database to allocate an Eircode PIK. In some cases, particularly when addresses were non-unique, it was not always possible to allocate an Eircode PIK. In these cases, for the purpose of IPEADS 2022, a Small Area Code was generally allocated. For the purpose of creating household and family statistics for this release, only those persons with an Eircode PIK allocated are included. Exclusions due to absence of Eircode PIKs only occurred in a very small number of cases.  

In summary, it was possible to directly assign an Eircode PIK from an administrative source to 94% of persons. The addition of Census Eircode PIKs brought this up to 98% and the matching exercise brought the percentage over 99%.

The key focus of the geocoding exercises was on a number of administrative data sets. These were:

  • Revenue Commissioners: Local Property Tax returns
  • Department of Social Protection: Central Records System
  • Department of Social Protection: Pandemic Unemployment Payments
  • Higher Education Authority: Third Level Enrolments
  • Health Service Executive: COVAX Dataset
  • Residential Tenancy Board: Tenancies
  • Student Universal Support Ireland: Further and Higher education grants

These datasets are regarded as robust sources of geography as they reflect activity close to or in the reference period used in this release. This means that the address data in these datasets is likely to be up to date. Some administrative data sets received by the CSO contain address information, but not an indicator as to whether the address is up to date or when it was last validated by the public sector body compiling it.

COVAX access is under Section 11 of the Statistics Act, 1993. It is important to note that COVAX vaccination data is only used for geocoding purposes and not as an activity indictor. The CSO’s use of COVAX data for official statistics is fully governed by CSO Data Protection protocols. The CSO’s access to sensitive and confidential health records is also underpinned by the written permission of the Minister for Health and provided for under Section 30 of the Statistics Act, 1993 – ‘Use of Records of Public Authorities for Statistical Purposes’. This permission has been duly granted by the Minister.

Using the geography information allocation described here, the CSO was able to develop two methodologies that estimate the number of Household Units in the State using administrative records. These methods are now described. Each method can be considered as a potential definition of households under administrative data.

Method One

Step 1. Allocate an Eircode PIK to persons as described in the Introduction.

Step 2. Take only those records with an Eircode PIK allocated.

Step 3. Group persons within unique Eircode PIKs to create Household Units. 

Method Two

Step 1. This begins by following steps 1, 2 and 3 from Method One.

Step 2. Isolate Household Units with under 7 persons allocated and create a Household Unit PIK based on unique Eircode PIKs.

Step 3a. Isolate household units with 7 or more persons allocated and:

Step 3b. Create separate Household Units by splitting persons into their unique Family Unit PIKs. For example, a household unit with 9 persons allocated with two unique Family Unit PIKs will now be considered as two Household Units of size four and five. Note that this split does not take place for Eircode PIKs where all persons are classified as “Single with No Children”.

Step 3c. Create a Household Unit PIK based on the result from Step 3b.

Step 4. Combine the results from Step 2 and Step 3c and group persons within unique Household Unit PIKs to create Household Units.

Interpreting Household Estimates

The methodology described above is developmental and this release is categorised as a CSO Frontier Series Output. Care must be taken when interpreting the statistics in this release. Since each method represents a different approach to defining households using administrative data, these are not directly comparable with Census household statistics.

Table 2: Household units by household size based on administrative data methodologies and Census of Population