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Background Notes

Background Notes

CSO statistical publication, , 11am

Background Notes

Purpose of Survey

The primary focus of the Survey on Income and Living Conditions (SILC) is the collection of information on the income and living conditions of different types of households in Ireland, in order to derive indicators on poverty, deprivation and social exclusion.  It is a voluntary survey (for selected households).  Up until 2020 the SILC was carried out under EU legislation (Council Regulation No 1177/2003) and commenced in Ireland in June 2003. On 01/01/2021 Council Regulation No 1177/2003 was repealed by Regulation (EU) 2019/1700.

Impact of the COVID-19 pandemic

The impact of the COVID-19 pandemic in terms of the operation of the SILC survey and on the subject matter itself is wide-ranging and is difficult to fully evaluate. Some key aspects that may have influenced the comparative results from 2020 and 2021 in this report are as follows:

Operational changes: Prior to the COVID-19 pandemic, respondents were recruited and all interviews were conducted in person. Interviewers would visit houses, often a number of times, to encourage sample households to take part. In March 2020 as the restrictions began, survey interviewing was paused for a couple of weeks and then moved to telephone interviewing (CATI) for the safety of both respondents and interviewers. The survey was quickly adapted for CATI and interviewers were set up to work from home. While we had contact details for waves 2 to 5 households, wave 1 respondents were recruited by post, inviting them to contact us. For 2022 and 2023, data collection was a mix of CAPI and CATI. These types of mode adjustments can have a significant impact on the distribution of the achieved sample. Indeed, we did see a distributional change in the tenure status for the responding households, for which we made an adjustment in the weighting. While the weighting process overall is designed to reflect society as a whole as much as possible, caution should be applied when making comparisons over time.

Behavioural changes: While temporary, societal adjustments in response to the pandemic and the consequential restrictions during 2020 and 2021 impacted the results of the survey in many ways. Some questions in SILC are subjective in nature and appear to have been influenced by the temporary conditions respondents found themselves in during lockdown. For example, the proportion that said they were Unable to afford a morning, afternoon or evening out in the last fortnight decreased 3.5 percentage points, from 7.5% in 2020 to 4.0% in 2021, while the proportion that were Unable to afford to have family or friends for a drink or meal once a month decreased from 10.3% in 2020 to 8.7% in 2021.  Though these indicators are designed to focus on affordability, the socially oriented nature of them may have been influenced by restrictions. Another example could be Principal Economic Status (PES), where a respondent may or may not have considered themselves Unemployed while on an income support scheme. The nature of many of these changes appear to have been temporary and should be interpreted with caution.

Break in Time Series

SILC has been running as an annual survey in Ireland since 2003. The changes in regulation across household surveys introduced by Regulation 2019/1700 provided us with an opportunity to review and revise SILC methodology throughout the collection, processing and analysis phases of SILC production. We introduced these changes for the 2020 SILC survey, and therefore the year 2020 represents a break in series for the survey. Please See Information Note - Break in Time Series SILC 2020.

Revisions

The annual Survey of Income and Living Condition (SILC) results are weighted using population estimates which are generated on an ongoing basis. Census of Population 2022 results have been used to revise population estimates for 2020 to 2022, and consequently results for SILC survey years 2020, 2021 and 2022 are revised. Please see the Information Note which compares published and revised results.

Reference Period

Information is collected from January to June with household interviews being conducted on a weekly basis. The income reference period for SILC is the previous calendar year. Therefore, the income referenced for the 2023 survey spans the period from January to December 2022.  In 2023, the achieved sample size was 4,191 households and 10,199 individuals.

Timeliness

The deprivation data for SILC 2022 was published in November 2022. The delay in publishing 2023 deprivation results was due to time required to produce 2020-2022 revised results.

Methodology

Rotational Sample Design

In 2022 the SILC sample moved from a 5-year to a 6-year rotational sample, with both a cross-sectional and a longitudinal element. Households interviewed for the first time are Wave 1 households.  Households who are interviewed in years are Wave 2 households (2nd year in the sample), Wave 3 households (3rd year in the sample), Wave 4 (4th year in the sample), Wave 5 (5th year in the sample), or Wave 6 (6th and final year in the sample). The initial sample design attempts to seed the sample with 20% for each new wave. However, due to non-response and sample attrition the waves are not evenly balanced in the sample with Wave 1 households usually tending to dominate.

Response Rates

The overall response rate for the SILC survey in 2023 was 36.9%.  The response rate is heavily influenced by the Wave 1 response rate which was 23.9% in 2023.  The response rates tend to be a lot higher for Wave 2-6 households and in 2023 the response rate for Wave 2-6 households was 59.2%.

Sample Design

In 2022 a new sampling methodology (which was further refined in 2023) was introduced to ensure SILC will be able to meet the precision requirements specified in the IESS regulation. Waves 1 and 2 of the SILC 2023 sample were selected using this methodology. In SILC 2023, Waves 3, 4,5 and 6 come from the 2018 sampling frame.

The following is a brief overview of the revised SILC sample methodology, from which Wave 1 of SILC 2023 was selected:

  • The SILC sample is a Stratified Simple Random Sample (SSRS).
  • The sample is stratified by county and 10 equivalised income bands.
  • Households were selected using probability proportional to size (PPS) of each strata.
  • The sampling frame is the 2016 Census, excluding households previously sampled for other social surveys.
  • Including longitudinal cases (waves 2-6), 12,000 households were selected for interview.

The Wave 1 sample methodology for SILC in 2022 was the same as the method used in 2023 with the following exception. In 2023, households were selected using probability proportional to size (PPS) of each strata. In 2022 households were selected using Neyman allocation. This involved allocating the sample across the strata according to the variability of income, where strata with large variance were allocated more of the sample.

The following is a brief overview of the 2014 SILC sample methodology, from which Waves 3-6 of SILC 2023 were selected:

  • The SILC sample is a multi-stage cluster sample resulting in all households in Ireland having an equal probability of selection.
  • The sample is stratified by NUTS4 and quintiles derived from the Pobal HP (Haase and Pratschke) Deprivation Index.
  • In the 2018 sample the clusters are based on Census Enumeration Areas, rather than the Household Survey Collection Unit Small Areas used in the 2014 sample.
  • A sample of 1,200 blocks (i.e. Census Enumeration Areas, Census 2016) from the total population of blocks is selected.
  • Blocks are selected using probability proportional to size (PPS), where the size of the block is determined by the number of occupied households on Census night 2016. 100 households from each block are selected at random to be retained for selection within each block.
  • All occupied households on Census night 2016 within each block are eligible for selection in the SILC sample.
  • Households within blocks are selected using simple random sampling without replacement (SRS) for inclusion in the survey sample.

Weighting

A design weight is assigned to each household which is calculated as the inverse proportion to the probability with which the household was sampled. 

Design weights are adjusted each year for each wave separately for non-response to bring the weights up to the current year. These weights are combined and scaled back and then calibrated to population totals for the current year. 

In accordance with Eurostat recommendation, CALMAR was used to calculate the household cross-sectional weights. Benchmark information was used to gross up the data to population estimates. The benchmark estimates were based on:

  • Age by sex: Individual population estimates are generated from population projections from census data. Age is broken down by 5-year age groups into seventeen categories.
  • Region: Household population estimates in each of the eight NUTS3 regions are generated using Labour Force Survey (LFS) data.
  • Household composition: 
    • 1 adult aged 65+, no children under 18
    • 1 adult aged <65, no children under 18
    • 2 adults, at least 1 aged 65+, no children under 18
    • 2 adults, both aged <65, no children under 18
    • 3+ adults, no children under 18
    • 1 adult, 1+ children under 18
    • 2 adults, 1-3 children under 18
    • Other households with children under 18
  • Tenure status: 
    • Owner-occupied: without outstanding mortgage
    • Owner-occupied: with outstanding mortgage
    • Rented, in receipt of HAP/RS/other rent subsidy
    • Rented, Local Authority
    • Rent free
    • Rented, without state housing assistance

Due to the “integrative” calibration method, the personal weight generated in CALMAR is equal to the household weight. Because there is no individual non-response within a household, the weights for personal cross-sectional respondents aged 16 and over are the same as the overall personal weight.

The target population for SILC are private households, and the persons living therein. As such, specific benchmark totals, to which the survey is calibrated, have been created to best reflect this.

The count of private dwellings is derived from Census, using interpolation and supplementary administrative data on new dwelling for intercensal years. To account for the shared income and expenditure definition of a household, a two-stage calibration process is used wherein the calibrated dwelling weights are applied to any multiple households within a dwelling.

For estimate of number of private household number, see below .

Age group2020202120222023
0-17 1,224,128 1,199,507 1,227,641 1,205,622
18-34 1,056,224 1,085,230 1,074,857 1,095,808
35-49 1,151,482 1,140,699 1,163,187 1,149,217
50-64 857,385 892,783 931,070 936,923
65+ 683,548 700,697 728,738 762,011
Total 4,972,768 5,018,916 5,125,493 5,149,582

The count of persons living private households is derived at by deducting estimates of persons outside the scope of SILC from the usually resident population estimates. Persons excluded from the SILC population benchmarks include those usually resident in hospitals; residential facilities for persons with mental and/or physical disabilities, nursing homes,  childrens' homes; religious communities; prisons; International Protection Accommodation Services (IPAS); homeless persons; persons fleeing the Ukraine under the Beneficiaries of Temporary Protection (BOTPs). During intercensal years, a combination of linear interpolation and administrative data is used to estimate the number persons outside the scope of SILC.

Household Composition2020202120222023
1 adult aged 65+ 174,219 179,327 184,736 190,708
1 adult aged <65 229,022 227,965 227,263 227,192
2 adults, at least 1 aged 65+ 210,274 216,924 223,942 231,642
2 adults, both aged <65 269,841 271,235 273,061 275,665
3 or more adults 299,792 306,852 314,422 322,932
1 adult with children aged under 18 76,808 76,813 76,940 77,283
2 adults with 1-3 children aged under 18 378,258 379,559 381,464 384,451
Other households with children aged under 18 190,083 191,946 194,118 196,851
Total 1,828,297 1,850,621 1,875,946 1,906,724

Precision estimates and statistical significance

Estimates were calculated in SAS using the Jackknife and the Taylor Linearisation methodology.  For the mean equivalised net disposable income, the ‘At Risk of Poverty’ rate, the ‘Deprivation’ rate and the ‘Consistent Poverty’ rate, the Jackknife Method in PROC SURVEYMEANS was used. The Taylor Linearisation Method in PROC SURVEYMEANS was used to measure the precision of the quantiles. 

SAS routines and macros were developed to calculate the precision of the more complex statistics, i.e. the Gini Coefficient and the Quintile Share Ratio (QSR), using the Jackknife Method.  The variance of the Gini and the QSR was estimated using the methodology outlined in Lohr1 Ch. 9 (Variance Estimation in Complex Surveys).  The calculations of the precision estimates took into account the weighting, the complex structure of the sample, (i.e. the fact that the sample was a cluster sample as opposed to a simple random sample) and other complications arising from the methods adopted.

When measuring the year-on-year change of a statistic, we take into account both the variance of the statistic in each year (sample) and the covariance of the statistic between samples.

See SILC Quality Report and SILC Background Notes for available precision estimates.

1Sampling: Design and Analysis, 2nd Edition, Sharon L. Lohr (2010).

Data collection

The annual SILC survey is the main data source for SILC. In response to growing concerns related to community transmission of COVID-19, the CSO suspended all household survey fieldwork activities in mid-March 2020. SILC information before the onset of COVID-19 was collected from household members (16 years and older) by CSO interviewers, using Computer-Assisted Personal Interview (CAPI) in the respondents' homes. In March 2020 the CSO developed a SILC data collection instrument suitable for conducting SILC longitudinal interviews by telephone (Computer-Assisted Telephone Interview (CATI)).   SILC 2023 data was collected via both CAPI and CATI from January to July 2023. Almost all household interviews were conducted by CAPI (4,153 out of 4,191 interviews).

In addition, CSO uses primary micro data sources in its statistical programs to complement or replace survey data, to make its statistical operations more efficient or to create new insights or products. These data enable CSO to fill information needs about the Irish society, economy and environment, reduce response burden and costs imposed by surveys, and improve data quality and timeliness. All data obtained by CSO are used solely for statistical purposes.

The primary micro data sources are the Department of Social Protection (DSP) social welfare data, Office of the Revenue Commissioners’ Income Tax Form 11 and PAYE Income data, Department of Agriculture, Food and the Marine Animal Identification and Movement Data, Student Universal Support Ireland Grant Application and Payment Data, Local Authority HAP Shared Services Centre Housing Assistance Payments and the Residential Tenancies Board Rent Data.  The CSO continues to work with these sources to ensure good quality data is available on a timely basis. 

Classifications and Indicators

 

Principal Economic Status

From 2020 the question on Principal Economic Status was standardised under Regulation (EU) 2019/1700.  The categories are:

  • Employed
  • Unemployed
  • Retired
  • Unable to work due to long-standing health problems
  • Student, pupil
  • Fulfilling domestic tasks

Highest Level of Edhouucation Completed

From 2020, the highest level of education achieved is mapped using the International Standard Classification of Education (ISCED 2011) coding system and categorised as follows:

ISCED codeHighest Level of Education Classification
000 Less than primary education Primary or below
100 Primary education
200 Lower secondary education Lower secondary (including transition year)
300 Upper secondary education (not further specified) Upper secondary
343 Level completion, without direct access to tertiary education
300 Upper secondary education (not further specified)
344 Level completion, with direct access to tertiary education
300 Upper secondary education (not further specified)
450 Vocational education Post leaving certificate
400 Post-secondary non-tertiary education (not further specified)
500 Short cycle tertiary Third level non-degree
600 Bachelor or equivalent Third level degree or higher
700 Master or equivalent
800 Doctorate or equivalent

Household composition

For the purposes of deriving household composition, a child was defined as any member of the household aged 17 or under. Households were analysed as a whole, regardless of the number of family units within the household. The categories of household composition are:

  • 1 adult aged 65+
  • 1 adult aged <65
  • 2 adults at least 1 aged 65+
  • 2 adults, both aged <65
  • 3 or more adults
  • 1 adult, with children aged under 18
  • 2 adults with 1-3 children aged under 18
  • Other households with children aged under 18

Household type

The categories of household type are:

  • One-person household
  • Lone parent with at least one child aged less than 25 years
  • Lone parent with all children aged 25 years or more
  • Couple without any child(ren)
  • Couple with at least one child aged less than 25 years
  • Couple with all children aged 25 years or more
  • Other type of household

Number of Persons at Work in the Household

The number of persons at work in the household is the number of persons that described their Principal Economic Status as Employed.

Tenure status

Tenure status refers to the nature of the accommodation in which the household resides. The status is provided by the respondent during the interview and responses are classified into the following two categories:

  • Owner-occupied
  • Rented or rent free

Urban/rural location

From 2020 onwards, areas are now classified as Urban or Rural based on the following area populations derived from Census of Population 2016:

Urban

  • Population >100,000
  • Population 50,000 – 99,999
  • Population 20,000 – 49,999
  • Population 10,000 – 19,999
  • Population 5,000 – 9,999
  • Population 1,500 – 4,999

Rural

  • Population 199 – 1,499
  • Rural areas in counties

Regions

The regional classifications in this release are based on the NUTS (Nomenclature of Territorial Units) classification used by Eurostat. The NUTS boundaries were amended on 21st November 2016 under Regulation (EC) No.2066/2016 and took effect from 1st January 2018. Results are presented at NUTS 2 level. See Information Note for Data Users: revision to the Irish NUTS 2 and NUTS 3 Regions.

Deprivation items

Households that are excluded and marginalised from consuming goods and services which are considered the norm for other people in society, due to an inability to afford them, are considered to be deprived. The identification of the marginalised or deprived is currently achieved on the basis of a set of eleven basic deprivation indicators:

  1. Without heating at some stage in the last year
  2. Unable to afford a morning, afternoon, or evening out in last fortnight
  3. Unable to afford two pairs of properly fitting shoes in good condition that are suitable for daily activities
  4. Unable to afford a roast once a week
  5. Unable to afford a meal with meat, chicken, fish, or vegetarian equivalent every second day
  6. Unable to afford new (not second-hand) clothes
  7. Unable to afford a warm waterproof coat
  8. Unable to afford to keep the home adequately warm
  9. Unable to afford to replace any worn out furniture
  10. Unable to afford to have family or friends for a drink or a meal once a month
  11. Unable to afford to buy presents for family or friends at least once a year

Enforced deprivation rate

Individuals who experience two or more of the eleven listed items are considered to be experiencing enforced deprivation. This is the basis for calculating the deprivation rate.

Additional deprivation items

Additional deprivation items were included in the 2023 SILC Enforced Deprivation publication. These deprivation items are not used to calculate the enforced deprivations rate.
• Unable to afford a one-week holiday away from home
• Unable to afford an unexpected expense without borrowing
• Unable to afford a car or van for private use
• Unable to afford to regularly participate in a leisure activity that costs money
• Unable to afford to spend a small amount of money most weeks on yourself for your own pleasure

Comparison with Eurostat EU-SILC estimates

Estimates produced from SILC data by the CSO are based on national definitions of income, equivalence scale, deprivation etc.  These are not directly comparable with EU-SILC estimates produced on the Eurostat website. 

Eurostat (the statistical office of the European Union (EU)) publish material and social deprivation indicator results for EU Member States, based on EU-SILC data. Eurostat’s material and social deprivation indicators are derived from a set of thirteen material deprivation items. The EU material and social deprivation rate is defined as the proportion of the population that is unable to afford five or more of the thirteen items. The EU severe material and social deprivation rate is defined as the proportion of the population that is unable to afford seven or more of the thirteen items. Six of the indicators Eurostat use to derive material and social deprivation rates are part of the set of eleven basic deprivation indicators used by Ireland to calculate the national enforced deprivation rate. These six indicators are:

  1. Eat meal with meat, chicken, fish (or vegetarian equivalent) every second day
  2. Replace any worn out furniture
  3. Keep the home adequately warm
  4. Buy new (not second-hand) clothes
  5. Two pairs of properly fitting shoes suitable for daily activities
  6. Getting together with friends/family for a drink/meal at least once a month

The additional seven deprivation indictors (used by Eurostat) that are not used in deriving national enforced deprivation rate are:

  1. Capacity to face unexpected expenses without borrowing
  2. Capacity to afford a one-week annual holiday away from home
  3. Having access to a car/van for personal use
  4. Having internet connection
  5. Spending a small amount of money each week on him/herself
  6. Capacity to afford to regularly participate in a leisure activity that costs money
  7. Capacity to avoid arrears (on mortgage or rental payments, utility bills, hire purchase instalments or other loan payments)

For further information please see the EU measure for severe material and social deprivation.

Calculation of Value for unexpected expense in SILC questionnaire

In the SILC survey, the respondent to the household questionnaire is asked ‘Can your household afford an unexpected expense of €X without borrowing? Note: If the payment was made on credit then the account should be debited within 1 month.’

The amount for €X in the survey question for the current years (time T) survey is 1/12th of the at-risk-of-poverty threshold for the survey conducted two years earlier (time T-2). The value of the at-risk-of-poverty (AROP) threshold is calculated by using the OECD modified equivalence scale and differs from the national at-risk-of-poverty threshold which uses a national equivalence scale for calculating equivalised income.   The national scale attributes a weight of 1 to the first adult, 0.66 to each subsequent adult (defined in this context as those aged 14+ living in the household) and 0.33 to each child aged less than 14. The OECD modified scale assigns a value of 1 to the first adult, 0.5 to each subsequent adult member and of 0.3 to each child. See Survey on Income and Living Conditions Fact Sheet (PDF 494KB)

In the 2023 SILC questionnaire the value for €X was €1,400. The answer given by the respondent of the household questionnaire is assigned to each person living in the household.

Acknowledgement

The Central Statistics Office wishes to thank the participating households for their co-operation in agreeing to take part in the SILC survey and for facilitating the collection of the relevant data.

For further information on this release:

E-mail ICW@CSO.ie or contact Brian Cahill (+353) 21 453 5173, or Paul Christopher (+353) 21 453 1441.