Persistent poverty in Scotland 2010-2024

5 Data source

This section provides key information on the data source and methodology used to produce persistent poverty statistics.

The estimates in this publication are derived from the Understanding Society survey. Understanding Society is a large scale longitudinal survey that captures information about social and economic circumstances, attitudes, behaviours and health. Being longitudinal, the same individuals are interviewed each year allowing identification of those who have been in poverty over a number of years rather than just at a single point in time.

The Understanding Society survey has longitudinal information for about 1,600 individuals in Scotland in 2020-2024. The survey is conducted by the University of Essex, and persistent poverty estimates are calculated by the Department of Work and Pensions (DWP) for the annual Income Dynamics publication. Detailed information on the method used to calculate persistent poverty estimates can be found on the UK government webpages.

Surveys gather information from a sample rather than from the whole population. Results from sample surveys are always estimates, not precise figures. This means that they are subject to a margin of error which can affect how changes in the numbers should be interpreted, especially in the short-term. Year-on-year movements should be treated with caution.  Further details can be found in Section 5.3.

5.1 Time periods

This publication presents persistent poverty rates for eleven overlapping periods, each consisting of four two-year periods (waves):

• 2010-2014: Jan 2010 - Dec 2011 (Wave 2) to Jan 2013 - Dec 2014 (Wave 5)
• 2011-2015: Jan 2011 - Dec 2012 (Wave 3) to Jan 2014 - Dec 2015 (Wave 6)
• 2012-2016: Jan 2012 - Dec 2013 (Wave 4) to Jan 2015 - Dec 2016 (Wave 7)
• 2013-2017: Jan 2013 - Dec 2014 (Wave 5) to Jan 2016 - Dec 2017 (Wave 8)
• 2014-2018: Jan 2014 - Dec 2015 (Wave 6) to Jan 2017 - Dec 2018 (Wave 9)
• 2015-2019: Jan 2015 - Dec 2016 (Wave 7) to Jan 2018 - Dec 2019 (Wave 10)
• 2016-2020: Jan 2016 - Dec 2017 (Wave 8) to Jan 2019 - Dec 2020 (Wave 11)
• 2017-2021: Jan 2017 - Dec 2018 (Wave 9) to Jan 2020 - Dec 2021 (Wave 12)
• 2018-2022: Jan 2018 - Dec 2019 (Wave 10) to Jan 2021 - Dec 2022 (Wave 13)
• 2019-2023: Jan 2019 - Dec 2020 (Wave 11) to Jan 2022 - Dec 2023 (Wave 14)
• 2020-2024: Jan 2020 - Dec 2021 (Wave 12) to Jan 2023 - Dec 2024 (Wave 15)

Persistent poverty statistics are based on tracking an individual over a four-year period. Each set of results are therefore based on four waves of the Understanding Society survey.  Each wave of interviews is conducted over a two-year period, and each individual is interviewed once every year.

There are known issues with the income information in the first Understanding Society wave covering 2009-2010. See the paper Does repeated measurement improve income data quality? (ISER Working Paper Series, 2016-11) by Paul Fisher for details of why income data on the first wave of Understanding Society are not comparable with subsequent waves and are likely to be of lower quality. The first wave has therefore been excluded from any analysis presented in this publication.

5.2 Population coverage

Understanding Society is a survey of private households (although it does collect information from households about their children if a child has moved into an institution). This means that people who were in residential institutions, such as nursing homes, barracks, prisons or university halls of residence at the start of the survey are excluded from the scope of the analysis presented here.

5.3 Reliability of estimates

Results from surveys are estimates and not precise figures - in general terms the smaller the sample size, the larger the uncertainty. DWP are unable to calculate sampling uncertainties for these statistics and often, it is better to look at trends over several periods to understand change.

As with most longitudinal surveys, attrition reduces the Understanding Society sample size over time. As well as attrition reducing the sample size, we have missing data for many of the variables we are using in the analysis. We exclude individuals with missing data from relevant analysis, but include individuals whenever we can. Weights have been applied which adjust for unequal selection probabilities, differential non-response, and potential sampling error.

5.4 Sample boosts

An Immigrant and Ethnic Minority Boost (IEMB) sample was included in the analysis for the 2023 report for the first time, improving previously published estimates. The inclusion of the IEMB has improved the representativeness of the statistics as well as increased the sample size of ethnic minority categories.

In 2022-2023 (Wave 14), a General Population Sample (GPS2) boost  was introduced into the Understanding Society survey in order to improve its representativeness. Members of the GPS2 boost have been included in the cross-sectional analysis from 2022 and 2023. Cross-sectional analysis is used to produce median incomes for each wave which are, in turn, used to measure who is in relative low income in that wave. This measurement forms the basis of ID’s longitudinal analysis of persistent low income, as well as analysis of low income entries and exits.

Now that members of the recent boost have had the opportunity to participate in two survey waves (Waves 14 and 15), they have, for this publication, been included in ID’s longitudinal analysis of low income entries and exits over the period 2022 and 2023 to 2023 and 2024.

Members of the boost cannot yet be included in the longitudinal sample used to measure rates of persistent low income, because they have not been present in the survey for enough time. The introduction of the GPS2 boost means that statistics involving survey data from 2022 and 2023 onwards are not fully comparable to those preceding them.

More information on how the GPS2 boost may affect the statistics can be found in Income Dynamics: Income movements and the persistence of low income, 2010-2024 published by DWP.

5.5 COVID-19 impact

The coronavirus pandemic affected fieldwork and data collection in some way during wave 11 (2019-2020), wave 12 (2020 to 2021), wave 13 (2021 and 2022) and wave 14 (2022 to 2023). Policy changes associated with the pandemic also resulted in some changes to income-related questions and will have affected household incomes during this period.

These impacts are detailed in the Background information and methodology section of the DWP report. Key points to note are:

• The first national lockdown due to the coronavirus pandemic began in March 2020, partway through waves 11 and 12.
• Before the lockdown, around two-thirds of the Understanding Society data collection was web-based, with around a third completed via face-to-face interviewing, and about 1% being conducted via telephone. Following lockdown, data collection for all respondents was swiftly moved online, with telephone follow-up used as necessary.
• Fieldwork figures show that the survey response rates were largely protected over this period: the response rate for April to December 2020 was just 1.5 percentage points lower than that of the same period in 2019. DWP were able to release a full set of tables for wave 12 with no additional detriment to sub-samples beyond the attrition that is usual for this type of longitudinal panel survey.
• With regards to waves 13 and 14 it was possible to reintroduce face-to-face interviewing in April 2022 following the lifting of pandemic-related restrictions.
• Adaptations made to the USoc questionnaire continued into wave 14. These enabled the survey to gather information on income-based support available to employees via the Coronavirus Job Retention Scheme (CJRS or ‘furlough’), and to the self-employed via the Self-Employment Income Support Scheme (SEISS). These changes were implemented from the end of July 2020. For more detailed information on how USoc adapted to the pandemic, please refer to Understanding Society Main Study changes due to the COVID-19 pandemic (wave 14 release).

5.6 Age groups

Whether an individual is counted as a child, working-age adult or pensioner is determined by their age during the first survey period. So, for example, an individual aged 15 in 2011 and aged 19 in 2015 will be counted as a child for the 2011-15 period.