{
  "abstract": "Background The UK possesses a large collection of longitudinal data utilised by researchers from multiple disciplines. However, there are no universal agreed definitions of what is meant by terms such as sample ‘coverage’, ‘representativeness’ and ‘external validity’ that are consistently applied across disciplines. We aimed to achieve consensus among experts across the disciplines of survey methodology, demography, statistics, epidemiology and public health on the meaning and use of such concepts.Methods This study used the Delphi method to establish consensus. First, a literature review identified key issues around the subject. A series of 34 Delphi statements were conceptualised by the research team and fielded in round one. The experts were asked to agree or disagree on a Likert-scale with the proposed statements under eight sections with the opportunity to add free text. Based on the responses and feedback received, a follow-up questionnaire was crafted with modified or new statements for round two. A final third iteration of the Delphi statements was fielded based on the responses and feedback from round two.Statements where consensus of 70% or more was reached were aggregated and presented to the participants in rounds two and three as consensus statements.Results A total of 86 experts were invited, mostlybut not exclusively UK-based. 35 experts (19 female and 16 male, 30 reported white ethnicity), with expertise in statistics, public health, demography, economics and quantitative methods, completed the first round with agreement or disagreement consensus reached (≥70%) on 16 out of the 34 statements. Twenty eight experts completed the second round which included 21 statements, with agreement on a further 6 statements. Twenty six experts completed the third round which included 12 statements (response rates 41%, 85% and 93% respectively). By the end of the third round, consensus was reached on 29 statements. Three further statements reached near consensus (agreement 65–68%) and two statements about the concept of ‘external validity’ achieved no consensus.Conclusion Consensus was reached across a range of disciplines with regards to the terms ‘coverage’ and ‘representativeness’. The term ‘external validity’appears to have different meanings across disciplines and consensus around this term was harder to reach. Our findings are likely to inform consistency on the language used to describe similar concepts and help longitudinal study design, interpretation of study findings, and science communications across health and social science disciplines.",
  "authors": [
    {
      "affiliations": [
        "Primary Care, Population Sciences and Medical Education, Faculty of Medicine, University of Southampton, Southampton, UK",
        "Applied Research Collaboration Wessex, University Hospital Southampton NHS Foundation Trust, Southampton, UK"
      ],
      "name": "Nisreen Alwan"
    },
    {
      "affiliations": [
        "School of Economic, Social and Political Sciences, University of Southampton, Southampton, UK"
      ],
      "name": "Ann Berrington"
    },
    {
      "affiliations": [
        "Primary Care, Population Sciences and Medical Education, Faculty of Medicine, University of Southampton, Southampton, UK"
      ],
      "name": "Aaron Vanam"
    },
    {
      "affiliations": [
        "School of Economic, Social and Political Sciences, University of Southampton, Southampton, UK"
      ],
      "name": "Olga Maslovskaya"
    },
    {
      "affiliations": [
        "Medical Research Council Lifecourse Epidemiology Centre, University of Southampton, Southampton, UK"
      ],
      "name": "Janis Baird"
    },
    {
      "affiliations": [
        "Medical Research Council Lifecourse Epidemiology Centre, University of Southampton, Southampton, UK"
      ],
      "name": "Nicholas Harvey"
    },
    {
      "affiliations": [
        "School of Economic, Social and Political Sciences, University of Southampton, Southampton, UK"
      ],
      "name": "Francesco Pantalone"
    },
    {
      "affiliations": [
        "School of Economic, Social and Political Sciences, University of Southampton, Southampton, UK"
      ],
      "name": "Peter Smith"
    },
    {
      "affiliations": [
        "School of Economic, Social and Political Sciences, University of Southampton, Southampton, UK"
      ],
      "name": "Paul Smith"
    }
  ],
  "title": "P77 Reaching consensus on representativeness and coverage in longitudinal population studies: a delphi study",
  "uid": "ab40907b-4e09-50e2-909c-168dff6d59d4"
}