The Population Sampled
The sample for data collection during 2021 was designed to be representative of the adult population aged 15+ of Great Britain. The survey population is estimated to be 53,927,883 according to JICPOPS mid 2021 projections based on 2011 census data. All details below relate to the sampling process for the 2021 survey.
Overview of the PAMCo Sample
PAMCo has a multi-stage disproportional pre-selected sample design.
The three stages of sampling are as follows:
- Selection of sampling points
- Selection of addresses
- Selection of individuals
The sampling frame for the selection of sampling points comprises all Output Areas (OAs) in Great Britain. Two OAs are selected per sampling point.
The sampling frame for the selection of addresses is the Postal Address File (PAF).
Data collection is divided into two stages, each with its own procedure for the selection of the household members to be sampled.
At an initial postal stage, three mailouts are sent by post to each address and any two household members aged 15+ are invited to complete the survey.
At the field stage Interviewers are issued with the addresses where there has been no survey completed (and no refusal to take part) at the postal stage. At each household contacted they enumerate eligible individuals aged 15+. The final stage of the sampling is then to select which of these eligible individuals should be interviewed. One individual is selected in most households, and up to two individuals in larger households. The rules as to how this is done are described later in this document.
Some disproportional sampling is used at the stage of selecting sampling points in order to over-sample certain ACORN areas particularly likely to contain individuals with AB social grades.
Selection of Sampling Points
The first stage of sampling is to select the sample points (or locations) where data collection will be carried out. Before this is done, certain ACORN areas are upweighted (and others downweighted). This is done so as to oversample areas where individuals with AB social grades are particularly likely to live, and therefore increase the number of interviews taken with AB participants.
The steps taken to select the sampling points are therefore as follows:
a) Sampling weights are applied to the adult populations of OAs by 7 categories of ACORN Types, as follows:
|Category||ACORN Types||Weights Applied|
|1||1, 2, 3||1.91|
|2||4, 5, 7, 8, 9, 14, 16||1.63|
|3||6, 10, 15, 17, 61||1.36|
|4||11, 12, 13, 18, 19, 20, 21, 22, 24, 26, 32, 62, 00||1.11|
|5||23, 25, 28, 29, 31, 33, 34, 37, 53, 54, 60||1.01|
|6||27, 30, 36, 38, 41, 49, 50||0.74|
|7||35, 39, 40, 42, 43, 44, 45, 46, 47, 48, 51, 52, 55, 56, 57, 58, 59||0.65|
b) Great Britain is divided into 60 area groupings, devised for PAMCo, individually weighted and used to piece together the Government Office Region and non-overlap ISBA TV regions.
A full list of the 60 areas can be found overleaf. For the purposes of sampling, the area groupings are further sub-divided into district groupings.
c) The weighted adult populations of each of the 60 area groupings are calculated. The target number of sampling points for each area grouping is then set. The total number of points at this stage is 1,616 per annum.
d) Within each area grouping, OAs are ranked in descending order by PAMCo district grouping, then within district by PAMCo ACORN category, and finally within PAMCo ACORN category by NS-SEC.
e) The required number of OAs within each area grouping as specified at b) is then selected with probability proportional to weighted adult populations, using random start/fixed sampling interval procedures.
f) Any selected OA falling into a ‘no-go’ area (as separately defined) is replaced with one in the sample District and same ACORN Type with population size closest to the originally selected OA.
g) Modified procedures are applied in Scotland in areas 49, 50, 51, 52, 56, 57, 58 and 59. In these areas the target number of points is increased, relative to other areas, to the numbers shown in the table overleaf.
The area groupings used and the target number of Sampling Points selected for data collection in 2021 are as follows:
England and Wales
|Area Groupings||Government Office Region||ISBA Area||No. of Points Selected|
|1||South West||South West||44|
|8||East of England||London||56|
|13||East of England||East of England||36|
|14||East Midlands||East of England||16|
|16||East of England||East of England||24|
|17||East of England||East of England||36|
|29||Wales||Wales and the West||8|
|30||Wales||Wales and the West||24|
|31||Wales||Wales and the West||28|
|33||South West||Wales and the West||20|
|34||South West||Wales and the West||36|
|35||Yorkshire and the Humber||Yorkshire||48|
|36||Yorkshire and the Humber||Yorkshire||28|
|37||Yorkshire and the Humber||Yorkshire||24|
|45||Yorkshire and the Humber||North East||16|
|46||North East||North East||28|
|47||North East||North East||12|
|48||North East||North East||12|
|Area Groupings||Area Names||No. of Points Selected
Allocation to Questionnaire Version
Each sampling point is assigned a code to determine the rotation order to be used to ask about the various newspapers and magazines during that particular assignment. For details of the rotation orders, see document entitled ‘The Interview’.
Selection of Addresses
Within each selected pair of OAs, 32 or 33 addresses are selected, apart from London where 35 addresses are selected.
At the field stage, addresses are issued to the interviewer via the Electronic Contact Sheet (ECS) software on their tablet computer.
A minimum of three calls is prescribed for each potentially productive address, of which at least one at the weekend and one on a weekday evening, before attempts to interview can be abandoned. Interviewers are encouraged to make as many calls as possible, varying them by time of day.
Selection of Individuals
The selection of individuals is done within the ECS using the following steps:
a) All selected addresses within each selected OA are allocated the letters P, Q, R and S consecutively.
b) For all issued addresses the ECS specifies the one or two persons to be interviewed, as follows:
|No. of adults at address||P||Q||R||S|
|3||Second||First, Third||Second, Third||First|
|4||First, Fourth||Second, Third||First, Fourth||Second, Third|
|5||Second, Fourth||First, Fifth||First, Third||Second, Fifth|
|6+||First, Youngest||Third, Fifth||Second, Fifth||Fourth, Youngest|
The ECS instructs interviewers to list all persons aged 15+ in a selected household, in descending order of age, and then confirms the person(s) selected for interview, depending on the total number of adults at the address and the letter allocated to that address.