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Methodology Used

Methodology Used

CSO statistical release, , 11am
Frontier Series Output

This release is categorised as a CSO Frontier Series Output. Particular care must be taken when interpreting the statistics in this release as it may use new methods which are under development and/or data sources which may be incomplete, for example new administrative data sources. For further information on the data sources, linking procedures and limitations of this report, see the Methodology and Background Notes sections.

Introduction to methodology

This new report 'A Review of Migration Indicators from Administrative Sources, Q3 2022 to Q2 2024' is a CSO Frontier Series release. It uses pseudonymised administrative data from public sector bodies to produce experimental estimates of immigration and emigration flows in Ireland in recent years, by sex, age and nationality. This experimental work uses novel methodologies in an attempt to estimate migration flows by measuring activity in some key administrative data sources.

This section gives an overview of the methodological approaches taken to producing migration estimates from administrative data. The results presented in this release are based on linking administrative data sets from a range of public service bodies. These datasets are listed in the Background Notes. A series of rules are then applied to decide who should be included in or excluded from the migration flows.

This project involves creating an estimate of the number of people migrating through the country on a quarterly basis. The rationale for this approach is that almost every person who is living in Ireland has some level of interaction with the State directly or indirectly, through a spouse or dependant, such as through taxation, benefit or pension payments or enrolment in education. Administrative data records from other government bodies allow the CSO to identify all persons who interacted with the State in each quarter. This presence of, or lack thereof, activity is then used as an indicator of being present in, or absent from, the country at that time.

It is important to note that the methodologies utilised in this report do not adhere to the official definition for migrants (as per the European Commission), as both short-term and long-term migrants are included in the immigration and emigration estimates and cannot be differentiated between.

The official definition of an immigrant (as per the European Commission) is a person who is arriving in a State with the intention to remain for a period exceeding a year. For emigrants the official definition  is a person, departing or exiting from one State intending to remain abroad for a period exceeding one year.

A person who moves to a country other than that of their usual residence for a period of at least three months but less than a year (12 months) except in cases where the movement to that country is for purposes of recreation, holiday, visits to friends or relatives, business, medical treatment or religious pilgrimage is considered a short-term migrant. An example of a short-term migrant is a seasonal worker.

Pseudonymisation

Before using personal administrative data for statistical purposes, the CSO removes all identifying personal information. This includes name, address and the Personal Public Service Number (PPSN), a unique number used by people in Ireland to access social welfare benefits, personal taxation and other public services. A pseudonymised Protected Identifier Key (PIK) is created by the CSO when the PPSN is removed. This PIK is unique and non-identifiable and is only used by the CSO.

Using these PIKs enables the CSO to link and analyse data for statistical purposes, while protecting the security and confidentiality of the individual data. All records in the matched datasets are pseudonymised and the results are in the form of statistical aggregates which do not identify any individuals.

Migration rules

The administrative data used in this report was not initially created for measuring migration, but rather for service delivery and day to day operations of public bodies. However, activity in administrative data can be a sign of presence in the State. A set of rules was developed to measure activity over a 4-quarter rolling period and assign migration status to individuals who meet certain criteria.

This paper uses two methodologies for indicators of migration from administrative sources. The main difference in these methodologies is the choice of datasets used. Method 1, the ‘base’ method, relies on a smaller set of datasets, primarily those available to the CSO in a more frequent and timely manner, thus allowing for a faster estimate to be calculated. These datasets include PMOD (PAYE data received from Revenue), DSP Payments (Social Welfare payments made by Dept of Social Protection) and PLSS (Solas course enrolments), as well as a lagged Child Benefit file which can be used to isolate young individuals who start showing activity on PMOD and DSP ensure these individuals are not included as a migrant flow.

Method 2 is the ‘base plus education’ method which uses all datasets mentioned above and includes 4 additional annual educational datasets; HEA (the Higher Education Authority), QQI (Quality and Qualifications Ireland), as well as Primary and Post-Primary education. The addition of these datasets results in a more holistic approach to capturing flows between the workforce and education within the country. This comes with a trade-off on timeliness and thus this method cannot be used for fast estimate calculations.

These rules varied depending on the frequency of the receipt of the dataset by the CSO. Some datasets, for example the Primary Online Database of primary school children, is received annually by the CSO. Other datasets, for example the PMOD dataset are received monthly. Having access to more frequent datasets facilitates more detailed rules to be applied in deciding on whether a person has migrated. Details on the frequency of receipt of each dataset used in this project are provided in the Background Notes.

Annual datasets

The key rule applied to annual datasets is that all persons appearing on these datasets are counted as present in the State for the dataset’s reference year.

Monthly datasets

The monthly datasets are grouped into their respective quarters before being analysed, i.e. Quarter 1 being January, February and March; Quarter 2 being April, May and June; Quarter 3 being July, August and September; and Quarter 4 being October, November and December.

Additional rules

Three further universal rules were applied to all datasets. These were:

  1. Persons aged under 1 year at the start of the reference quarter are excluded from the count;
  2. Persons who died on or before the start of the reference quarter were excluded from the count;
  3. Young persons who were present on the Child Benefit payment file in the two calendar years prior to the reference quarter were excluded from the migrant flows if they are captured by the activity rule.

Identifying migrant cohorts

There are three distinct cohorts of migrants who appear in this release:

  1. New Inward Migrants: These are individuals who receive a PPSN upon entering the country for the first time and proceed to show activity in the selected State datasets within the reference quarter or the following quarter. The newly created PPSNs which belong to individuals who do not show activity but show a relationship with an active PPSN are also included in this group.
  2. Returning Inward Migrants: These are individuals who already have a PPSN but have not shown any activity in the selected State datasets in at least the two quarters preceding the reference quarter. The second criterion that these individuals must meet is that they proceed to show activity in the quarter following the reference quarter also.
  3. Outward Migrants: These are individuals who have been showing activity in the selected State datasets for both quarters preceding the reference quarter. In both the reference quarter and the quarter following this, the individual must show no activity in the selected State datasets.

Any individuals who do not meet the above criteria are not included in the migration flows.

Limitations of methodologies

There are two main limitations in this developmental release.

The first of these is that it is not possible to determine if an individual is a long-term or a short-term migrant. This is due to a trade-off between timeliness of reporting and the ability to match the usual residence definition.

Secondly, both of these methodologies have difficulties capturing certain cohorts of migrants. Due to this, some individuals may be misclassified depending on the method used. Some of these cohorts are as follows:

  • International students who do not require a PPSN cannot be traced using these methodologies.
  • Self-employed individuals are not accounted for; this means that an individual may appear in a migrant flow if moving between self-employed and PAYE employment.
  • Individuals who receive State payments from abroad (e.g. pensions) could be included in the migrant flows.
  • Individuals who are in the country but not interacting with the selected State services cannot be included in the flows.
  • Method 1, cannot easily track third level national students using available datasets. Method 2’s introduction of educational datasets combats this issue.
  • In both methods an individual might appear in both inward and outward flows over the 8-quarter retrospective period due to their administrative activity patterns.

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