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In search of a population sampling frame for UK postal surveys

In search of a population sampling frame for UK postal surveys. Gerry Nicolaas and Sarah Tipping. Acknowledgements. Our sponsors: The Socio-economic Inequalities Branch (SEIB), Office for National Statistics Our collaborators at the Office for National Statistics:

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In search of a population sampling frame for UK postal surveys

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  1. In search of a population sampling frame for UK postal surveys Gerry Nicolaas and Sarah Tipping

  2. Acknowledgements Our sponsors: The Socio-economic Inequalities Branch (SEIB), Office for National Statistics Our collaborators at the Office for National Statistics: Amanda Wilmot, Abigail Dewar, Zeeshan Rahman, Colin Hand

  3. Postcode Address File (PAF) • List of all addresses to which mail is sent • Small user file (less than 50 mail items per day) • 10% of addresses are non-residential • Almost complete coverage • Most commonly used sampling frame for major surveys • Sample of addresses, NOT individuals • No names!

  4. Electoral Register (ER) • List of eligible adults aged 18+ registered to vote • Can be used to sample individuals • Includes names as well as addresses • Coverage problems!

  5. Coverage problems of ER: • Does not include people who are not eligible to vote • Does not include people who fail to register • Does not include people who opt out of the publicly available version of the ER (the edited ER)

  6. Commercial alternatives: • CACI’s Consumer Register • Experian’s National Canvasse • Equifax’ ConnectSelect • EuroDirect’s Data Exchange • NB. These databases were not developed for probability sampling of the general population.

  7. CACI’s Consumer Register: • Edited Electoral Register • Supplemented with data from Claritas, DataWorks, Bounty’s market leading mother and baby file, large mail order databases • Updated quarterly • Includes names and addresses • Also includes information which could possibly be used for sampling, e.g. modelled age • Claims to be the most comprehensive database • Almost 40 million names and addresses of UK adults

  8. Design of the study: • Sample of 6,030 PAF addresses in GB selected for the ONS Omnibus Survey (April - June 2005) • Names from CACI’s Consumer Register matched to sampled PAF addresses • Omnibus interviewers collected household grid information for responding cases, including first name, sex and age • Manual matching of Consumer Register names with names from the household grid • Omnibus household grid treated as “correct”

  9. Individuals at responding addresses Correct name & address 2,350 4,436 Incorrect name & address - 1,050 Not on CR On CR

  10. Individuals at responding addresses Correct name & address 2,350 4,436 6,784 (35%) (65%) Incorrect name & address - 1,050 Not on CR On CR

  11. Individuals at responding addresses Correct name & address 2,350 4,436 (81%) 5,486 Incorrect name & address - 1,050 (19%) Not on CR On CR

  12. Characteristics of adults aged 18+ not included on the CR: • Sex distribution is not significantly different • More likely to be aged 18-24 • More likely to be renting their accommodation • More likely to have a degree

  13. If sampling adults aged 18+ from Consumer Register: • 35% of all adults aged 18+ in GB are not included on the CR • Under-representation of specific groups may bias survey results • 19% of adults sampled from CR will not be found at address

  14. BUT…….. • Is the Consumer Register a better sampling frame for general population surveys than the edited Electoral Register? • NB. 86% of adults listed on the Consumer Register were also listed on the edited Electoral Register

  15. Individuals at responding addresses Correct name & address 2,929 3,857 Incorrect name & address - 861 Not on edited ER On edited ER

  16. Individuals at responding addresses Correct name & address 2,929 3,857 6,786 (43%) (57%) Incorrect name & address - 861 Not on edited ER On edited ER

  17. Individuals at responding addresses Correct name & address 2,929 3,857 (82%) 4,718 Incorrect name & address - 861 (18%) Not on edited ER On edited ER

  18. Sample of individuals Consumer Register % 19 65 Edited ER % 18 57 Not found at address Coverage of adults aged 18+ in GB

  19. Sample of responding individuals Edited Electoral Register % 44 4 21 16 5 2,128 Consumer Register % 44 3 20 16 5 2,444 PAF % 45 6 27 18 7 3,709 Male Aged 18-24 Renting Degree Non-white Bases

  20. Conclusion: • CR has greater coverage of GB adults than edited ER • BUT • not much greater (57% on edited ER and 65% on CR) • no improvement in sample representativeness

  21. So the search continues……. • Other commercial databases? • Combine commercial databases? • Mixed mode? • Personalised and unpersonalised mailings? • ……….

  22. Limitation of study: • We have assumed that the matching rate at the individual level was the same for responding and non-responding households • BUT • this doesn’t have impact on comparison between PAF, edited ER and CR • estimated coverage rate is likely to be an overestimate

  23. For further information: • Gerry Nicolaas • tel. 020 7549 9567 • email G.Nicolaas@NatCen.ac.uk • Amanda Wilmot • tel. 020 7533 5321 • email Amanda.Wilmot@ons.gsi.gov.uk

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