Errors in reported degrees and respondent driven sampling: Implications for bias

Harriet L Mills, Samuel Johnson, Matthew Hickman, Nick S. Jones, Caroline Colijn

Research output: Contribution to journalArticle (Academic Journal)peer-review

24 Citations (Scopus)


Background: Respondent Driven Sampling (RDS) is a network or chain sampling method designed to access individuals from hard-to-reach populations such as people who inject drugs (PWID). RDS surveys are used to monitor behaviour and infection occurence over time; these estimations require adjusting to account for over-sampling of individuals with many contacts. Adjustment is done based on individuals' reported total number of contacts, assuming these are correct.

Methods: Data on the number of contacts (degrees) of individuals sampled in two RDS surveys in Bristol, UK, show larger numbers of individuals reporting numbers of contacts in multiples of 5 and 10 than would be expected at random. To mimic these patterns we generate contact networks and explore different methods of mis-reporting degrees. We simulate RDS surveys and explore the sensitivity of adjusted estimates to these different methods.

Results: We find that inaccurate reporting of degrees can cause large and variable bias in estimates of prevalence or incidence. Our simulations imply that paired RDS surveys could over- or under-estimate any change in prevalence by as much as 25%. These are particularly sensitive to inaccuracies in the degree estimates of individuals with who have low degree.

Conclusions: There is a substantial risk of bias in estimates from RDS if degrees are not correctly reported. This is particularly important when analysing consecutive RDS samples to assess trends in population prevalence and behaviour. RDS questionnaires should be refined to obtain high resolution degree information, particularly from low-degree individuals. Additionally, larger sample sizes can reduce uncertainty in estimates. (C) 2014 The Authors. Published by Elsevier Ireland Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)120-126
Number of pages7
JournalDrug and Alcohol Dependence
Publication statusPublished - 1 Sep 2014

Bibliographical note

Copyright © 2014 The Authors. Published by Elsevier Ireland Ltd.. All rights reserved.


  • Respondent driven sampling
  • At-risk populations
  • Contact network size
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