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Background Notes

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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 (for selected respondents) survey of private households.  It is carried out under EU legislation (Council Regulation No 1177/2003) and commenced in Ireland in June 2003.  

Reference period

Information is collected continuously throughout the year with household interviews being conducted on a weekly basis. The income reference period for SILC is the 12 months immediately prior to the date of interview. Therefore, the income referenced spans the period from January 2018 to December 2019.  In 2019, the achieved sample size was 4,183 households and 10,698 individuals.


For 2019, the results for enforced deprivation of the SILC survey were published nine months after the end of the reference period and eight months after the end of the data collection period. 

Rotational Sample Design

The SILC sample is a rotational sample. In 2018, a new sample was introduced.  This means that waves 1 and 2 for the 2019 SILC comes from the 2018 sampling frame, while waves 3 and 4 come from the 2014 sampling frame.

There is both a cross-sectional and a longitudinal element to the SILC sample. Households interviewed for the first time are Wave 1 households.  Households who are interviewed in subsequent years are Wave 2 households (2nd year in the sample), Wave 3 households (3rd year in the sample) or Wave 4 (4th and final year in the sample). The initial sample design attempts to seed the sample with 25% 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. 

The CSO has strengthened its own rules and procedures around sample implementation.  One of the key improvements in sample implementation over the past number of years is the ruling out of the substitution of households by interviewers. 

Response Rates

The overall response rate for the SILC survey in 2019 was 40%.  The response rate is heavily influenced by the Wave 1 response rate which was 29% in 2019.  The response rates tend to be a lot higher for Wave 2-4 households and in 2019 the response rate for Wave 2-4 households was 70%.

Sample design

In 2014, a new sampling methodology was introduced to improve the robustness of the SILC Sample. The sample methodology takes into account response rates and attrition rates to ensure the CSO achieves the required effective sample size required by Eurostat.  In 2018, a new sample was introduced.  This means that waves 1 and 2 for the 2019 SILC comes from the 2018 sampling frame, while waves 3 and 4 come from the 2014 sampling frame. The following is a brief overview of the revised SILC sample methodology:

  • 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.
  • 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.


A design weight is assigned to each household which is calculated as the inverse proportion to the probability with which the household was sampled. For SILC, the probability of the selection of a household is based on two elements; the probability of the selection of a block and the probability of selection of a household within that block. The design weights were calculated separately for each wave.

For Waves 1 households, the design weights were calculated as outlined above and adjusted so as to be proportional to the 2019 sample as a whole.  For Wave 2-4 households, base weights were calculated by firstly adjusting the personal weights from the previous year for non-response. The Weight Share Method was then applied to calculate a base weight for the household. These design weights were then adjusted so as to be proportional to the original sample as a whole.

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 into four categories: 0-14, 15-34, 35-64 and 65 and over.
  • Region: Household population estimates in each of the eight NUTS3 regions are generated using Labour Force Survey (LFS) data.
  • Household composition: Household composition estimates are also generated from the LFS. The following categories are used:

¨       One adult, no children

¨       Two adults, no children

¨       Three or more adults, no children

¨       One adult, one or more children

¨       Two adults, one to three children

¨       Other households with children

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.

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.

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

Data collection

The annual SILC survey is the main data source for SILC. Information is collected from all household members on laptop computers by trained interviewers, using Computer-Assisted Personal Interview (CAPI) software. 

In addition, the CSO has two primary micro data sources.  These are the Department of Social Protection (DSP) social welfare data and Revenue Commissioners’ employee income data.  The CSO continues to work with DSP and Revenue to ensure good quality data is available on a timely basis. 

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

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 three categories:

  • Owner-occupied
  • Rented at the market rate
  • Rented at below the market rate or rent free (includes Local Authority housing, rent-free lettings or rents agreed at below the market rate)

Urban/rural location

From 2014 onwards due to the new sampling methodology, areas are now classified as Urban or Rural based on the following population densities derived from Census of Population 2016:


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


  •       Population density <199 – 999
  •       Rural areas in counties

Prior to 2014, areas were classified as Urban or Rural based on the following population densities:


  •      Cities
  •      Suburbs of cities
  •      Mixed urban/rural areas bordering on the suburbs of cities
  •      Towns and their environs with populations of 5,000 or over (large urban)
  •      Mixed urban/rural areas bordering on the environs of larger towns
  •      Towns and their environs with a population of 1,000 to 5,000 (other urban)


  •      Mixed urban/rural areas
  •      Rural areas. 


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. As a result, new NUTS (regional classification) groupings have been introduced for Ireland. As the CSO weights results in the SILC using NUTS3 groups, survey estimates have been revised for SILC years 2012-2016 to take account of these changes. This reweighted data from 2012 to 2016 inclusive was published with the SILC 2017 results and users should note that there is a break in the regional data series from 2012 as the results for the period 2004 to 2011 are published using the old NUTS groupings.



Deprivation rate

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. Two pairs of strong shoes
  2. A warm waterproof overcoat
  3. Buy new (not second-hand) clothes
  4. Eat meal with meat, chicken, fish (or vegetarian equivalent) every second day
  5. Have a roast joint or its equivalent once a week
  6. Had to go without heating during the last year through lack of money
  7. Keep the home adequately warm
  8. Buy presents for family or friends at least once a year
  9. Replace any worn out furniture
  10. Have family or friends for a drink or meal once a month
  11. Have a morning, afternoon or evening out in the last fortnight for entertainment

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.


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:


Eva O’Regan (+353) 21 453 5243, or Kathryn Foskin (+353) 21 453 5302

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Background Notes

One in ten single-parent households could not afford to pay for school trips

CSO statistical publication, , 11am