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Cited by 176Delphi Technique in ResearchMeta-analysis and systematic reviewsReliability and Agreement in Measurement

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Sample size in multistakeholder Delphi surveys: at what minimum sample size do replicability of results stabilize?

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Manyara, Anthony Muchai, Purvis, Anthony, Ciani, Oriana, Collins, Gary S., Taylor, Rod S.·2024·Journal of Clinical Epidemiology
DOI 10.1016/j.jclinepi.2024.111485PMC PMC7617918
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Abstract

BACKGROUND AND OBJECTIVE: The minimum sample size for multistakeholder Delphi surveys remains understudied. Drawing from three large international multistakeholder Delphi surveys, this study aimed to: 1) investigate the effect of increasing sample size on replicability of results; 2) assess whether the level of replicability of results differed with participant characteristics: for example, gender, age, and profession. METHODS: We used data from Delphi surveys to develop guidance for improved reporting of health-care intervention trials: SPIRIT (Standard Protocol Items: Recommendations for Interventional Trials) and CONSORT (Consolidated Standards of Reporting Trials) extension for surrogate end points (n = 175, 22 items rated); CONSORT-SPI [CONSORT extension for Social and Psychological Interventions] (n = 333, 77 items rated); and core outcome set for burn care (n = 553, 88 items rated). Resampling with replacement was used to draw random subsamples from the participant data set in each of the three surveys. For each subsample, the median value of all rated survey items was calculated and compared to the medians from the full participant data set. The median number (and interquartile range) of medians replicated was used to calculate the percentage replicability (and variability). High replicability was defined as ≥80% and moderate as 60% and <80% RESULTS: The average median replicability (variability) as a percentage of total number of items rated from the three datasets was 81% (10%) at a sample size of 60. In one of the datasets (CONSORT-SPI), a ≥80% replicability was reached at a sample size of 80. On average, increasing the sample size from 80 to 160 increased the replicability of results by a further 3% and reduced variability by 1%. For subgroup analysis based on participant characteristics (eg, gender, age, professional role), using resampled samples of 20 to 100 showed that a sample size of 20 to 30 resulted to moderate replicability levels of 64% to 77%. CONCLUSION: We found that a minimum sample size of 60-80 participants in multistakeholder Delphi surveys provides a high level of replicability (≥80%) in the results. For Delphi studies limited to individual stakeholder groups (such as researchers, clinicians, patients), a sample size of 20 to 30 per group may be sufficient.

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Figure Boxplots showing replicability of results with increasing sample size in the three datasets: random resampled samples (20-500) on the x-axis and the median number of medians replicated (median replicability) from the full sample ratings (y-axis). Note for each panel, the maximum value of the y-axis is the number of items in each survey (22 for SPIRIT|CONSORT-Surrogate, 77 for CONSORT-SPI and 88 for COSB-i, respectively)).
Figure Boxplots showing replicability of results with increasing sample size in the three datasets: random resampled samples (20-500) on the x-axis and the median number of medians replicated (median replicability) from the full sample ratings (y-axis). Note for each panel, the maximum value of the y-axis is the number of items in each survey (22 for SPIRIT|CONSORT-Surrogate, 77 for CONSORT-SPI and 88 for COSB-i, respectively)).CC BY · PubMed Central

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Metadata

Authors
Manyara, A. M., Purvis, A., Ciani, O., Collins, G. S., & Taylor, R. S.
Affiliations
  • University of Bristol (GB)
  • University of Glasgow (GB)
  • Bocconi University (IT)
  • MRC/CSO Social and Public Health Sciences Unit (GB)
Corresponding author
Manyara, Anthony Muchai
ORCID
Venue
Journal of Clinical Epidemiology
Publisher
Elsevier BV
Published
2024-10
Volume
174
Pages
111485
ISSN
0895-4356 (ISSN-L)
DOI
10.1016/j.jclinepi.2024.111485
PMC
PMC7617918
OpenAlex
W4401027269
Cited by
163
References
36
Citations by year
2026: 93 · 2025: 67 · 2024: 3
FWCI
116.49
Type
journal article
Language
en
Open access
Licence
Locations
  • Journal of Clinical Epidemiology (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • University of Birmingham Research Portal (University of Birmingham) (publishedVersion, cc-by)
  • ENLIGHTEN (Jurnal Bimbingan dan Konseling Islam) (acceptedVersion, cc-by-sa)
  • PubMed Central (acceptedVersion, cc-by)
  • Archivio istituzionale della Ricerca - Bocconi (submittedVersion, cc-by-nc-nd)
  • Explore Bristol Research (submittedVersion, cc-by)
Funders
  • Cancer Research UK (C49297/A27294)
  • Economic and Social Research Council
  • National Institute for Health and Care Research
  • UKRI MRC (MR/V038400/1, 304823-01)
Topics
  • Social Sciences › Sociology and Political Science › Delphi Technique in Research
  • Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
  • Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Reliability and Agreement in Measurement
Keywords
sample size, minimum sample size, resampling, participant characteristics, gender, age, professional roles, reporting guidelines, alcoholic beverages, core outcome set, burn treatment, surrogate endpoints, stakeholder consensus, subgroup analysis
MeSH terms
Adult, Delphi Technique, Female, Humans, Male, Middle Aged, Surveys and Questionnaires, Research Design, Reproducibility of Results, Sample Size

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