Growing up In Ireland Cohort ’98 (Child Cohort)
Wave 4 - 20 years, 2019

Study number (SN): 0020-04


Central Statistics Office (CSO). (2021). Growing up In Ireland Cohort ’98 (Child Cohort) Wave 4 - 20 years, 2019. [dataset]. Version 1. Irish Social Science Data Archive. SN: 0020-04. URL



Growing Up in Ireland - the National Longitudinal Study of Children is a landmark study of children and youth which has been running since 2006. The objectives of the study are outlined in a separate publication (Greene et al. 2010). In summary, the project seeks to further our understanding of what it means to be a child or young person growing up in modern Ireland, with a view to informing policy on what both helps and hinders development. A two cohort, cross-sequential longitudinal design was adopted and began with one cohort (Cohort ‘08) of 11,134 infants (aged 9 months) and a second cohort (Cohort ‘98) of 8,568 9-year-olds. Being longitudinal in nature, the same participants are followed over time. The families of Cohort ‘08 have been interviewed when the children were 9 months, 3 years, 5 years and subsequently 9 years of age, while Cohort ’98 and their parents/guardians were interviewed at 9, 13 and 17/18 years of age.
This wave of data concerns the Wave 4 interviews of Cohort ‘98 at 20 years of age. As the 20-year-olds are now adults, they are regarded as the main respondents. One parent was also asked to complete questionnaires.

These data have been collected by Growing Up in Ireland, the national longitudinal study of children and young people. The study is funded by Government and the Department of Children, Equality, Disability, Integration and Youth (DCEDIY) is the project sponsor.  The study is carried out by the GUI Research Team at DCEDIY, in partnership with the Central Statistics Office (CSO).  The Department leads on research aspects of GUI, such as identifying data needs in advance of each wave, and conducting or commissioning policy relevant analyses of available data; and the CSO leads on GUI data collection and the production of statistical outputs.  GUI data are collected under the strict confidentiality requirements of the Statistics Act 1993


  • Families
  • Young Adults
  • Health
  • Mental Health
  • Identity
  • Cognitive Processes
  • Education
  • Employment
  • Income and Expenditure
  • Leisure Time Activities
  • Parental Role
  • Anthropometric Measurements



Cohort ’98 were born between 1st November 1997 and the 31st October 1998 and were aged 9 years at the time of the first data collection between August 2007 and May 2008. Over 8,000 families participated in the first wave (n=8,568) while 7,525 took part at age 13 years (Aug 2011 - March 2012), and 6,216 at age 17/18 years (April 2015 – Aug 2016). The current fourth wave of data collection, took place between August 2018 and June 2019, when the cohort was 20 years of age and was completed by 5,190 20-year-olds.

Observation units

  • Families / Households

Temporal coverage

From 08/2018 to 06/2019

Time dimension

Cohort study

Geographical coverage

Country: Ireland

Methods of data collection

  • CAPI (Computer Aided Personal Interviewing)
  • CASI (Computer Assisted Self Interviewing)

Sampling procedures

Full details on the population, sampling frame and sample design for the Child Cohort are given in a dedicated publication entitled Sample Design and Response in Wave 1 of the Child Cohort of Growing Up in Ireland.

A two-stage design was adopted. In the first instance a random sample of Primary Schools was recruited and at the second stage a sample of nine-year old children was selected from the sample of schools. The design required that the sample be regionally representative with no spatial bias. In addition, no oversampling or booster sampling of subgroups was required. There was a total of 56,497 nine-year-olds registered in the Census of Population in 2006 so a sample size of 8,568 represented approximately 14 percent or about 1 in every 7 of the nine-year-olds resident in the country.

For Wave 4 (at age 20) the Study Team approached all previous participants unless the family had previously definitively refused to be contacted in future waves of the study or was not eligible (i.e. the whole family had moved abroad or the young adult was sadly deceased). In total, contact details for 7,925 20-year-olds were issued to interviewers in Wave 4. Questionnaires were completed by 5,190 20-year-olds (the main respondents in this wave), which represented 65 per cent of the cases issued to interviewers.

The Young Adult (formerly known as Study Child or Young Person) is the longitudinal focus of Growing Up in Ireland. We are interested throughout the study in tracking, interviewing, measuring and testing the Young Adult, regardless of changes in his/her family composition, structure or geographical location. In this respect the study is based on a pure, fixed panel of participants who were 9 years of age at the time of first interview. After the initial sample recruitment, no additions were made to the sample, with the only loss being through interwave non-response or attrition (including moving outside the jurisdiction) and children who deceased between waves of interviewing. Therefore, the longitudinal population in the study is the population of 9-year-olds (and their main Caregivers) who were resident in Ireland at Wave 1 and who continued to be resident in Ireland at Waves 2, 3 and 4.

Response rate

In total, contact details for 7,925 20-year-olds were issued to interviewers in Wave 4. Questionnaires were completed by 5,190 20-year-olds (the main respondents in this wave), which represented 65 per cent of the cases issued to interviewers.


A standard iterative procedure was used to generate the weights used in all phases of Growing Up in Ireland. This was implemented using software (known as the GROSS1 system) which was developed for the ESRI. The GROSS system is based on a minimum information loss algorithm which fits population marginals to sample totals within a regression framework and adjusts the sample according to pre-specified characteristics to ensure that it produces estimates which match population totals.

The sample weights for the data recorded with the 20-year-olds were constructed by first generating an inter-wave attrition weight to adjust the composition of the completed Wave 4 sample (20 years of age) to the Wave 3 sample (17/18-year-olds) by controlling for variations in Wave 4 response and attrition according to:

• Young Adult’s gender
• Level of education of Parent One
• Family type
• Number of children at age 9 (1-2, 3, 4+)
• Household Social Class
• Household equivalised income quintile
• Work status of Parent One (and Parent Two, where present)
• Young Adult’s Score (quintiles) on the Drumcondra Reading Test when they were 9 years old

In developing the attrition weight, variations in response patterns according to other family and child characteristics were investigated. The 8 characteristics identified above, however, were found to be the most systematically predictive of response in Wave 4.

When the Wave 4 sample was adjusted by the attrition weight, a new Wave 4 weighting factor was generated by taking the product of the attrition weight between Waves 3 and 4 and the Wave 3 weighting factor assigned to each young person (17/18-year-old) in the Wave of the study. The reader should note that the Wave 3 weight, in turn, incorporated the differential response at Waves 1 and 2.

The weighting factor which should be used with the sample 4,729 cases who participated at all waves (9 years, 13 years, 17/18 years and 20 years) is WGT_20YRb.

An additional 461 families who participated at 9 years but who did not participate at 13 and/or 17/18 years re-entered the sample at 20 years of age. These additional cases mean that a total of 5,190 cases are available for analysis of change between 9 and 20 years of age or if the data are being used cross-sectionally at 20 years.

A separate weighting factor has been generated for use with the slightly larger dataset of 5,190 20-year-olds and is called WGT_20YRa

For more details on sample design and data construction see:
A Summary Guide to Wave 4 of the Child Cohort (at 20 Years) of Growing Up in Ireland


Data (available through ISSDA application process)

File name

File format/s

Contents of file







Survey data using questionnaire-based variable naming


Documentation (available for download)

File name

File format/s

Contents of file



Cohort ’98 at 20 Years Codebook for Wave 4 of the Child Cohort



Summary Data Dictionary for Wave 4 of the Child Cohort (at 20 years)




Questionnaires for Wave 4 of the Child Cohort (at 20 years)



A Summary Guide to Wave 4 of the Child Cohort (at 20 years)





Accessing the data

To access the data, please complete a ISSDA Data Request Form for Research Purposes, sign it, and send it to ISSDA by email.

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Data will be disseminated on receipt of a fully completed, signed form. Incomplete or unsigned forms will be returned to the data requester for completion.


Department of Children, Equality, Disability, Integration and Youth


Any work based in whole or part on resources provided by ISSDA, should  acknowledge: "Growing up In Ireland Cohort ’98 (Child Cohort) Wave 4 - 20 years, 2019" and also ISSDA, in the following way: “Accessed via the Irish Social Science Data Archive -”.

Citation requirement

The data and its creators shall be cited in all publications and presentations for which the data have been used. The bibliographic citation may be in the form suggested by the archive or in the form required by the publication.

Bibliographical citation

Central Statistics Office (CSO). (2021). Growing up In Ireland Cohort ’98 (Child Cohort) Wave 4 - 20 years, 2019. [dataset]. Version 1. Irish Social Science Data Archive. SN: 0020-0. URL


The user shall notify the Irish Social Science Data Archive of all publications where she or he has used the data.