UNAIDS Reference Group Consultation

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Contents

UNAIDS Reference Group Consultation on Population Size Estimation Based on Respondent-driven Sampling

June 9 - 10, 2014

Venue: University of Massachusetts –Amherst, hosted by the Statistics Department and Krista Gile

Who: The consultation is called by the UNAIDS Reference Group on Estimates, Modelling and Projections. We are inviting a diverse group of field implementers, end data users, and statisticians/mathematicians.

Goal: Obtain methods that may yield valid population size estimates using data from chain referral sampling. Current methods are largely considered “good enough” at best. We are looking for additions to the tool box, preferably better ones.

Key objectives:

  • Determine whether the Handcock-Gile-Mar method yields reasonable size estimates in comparison

with existing methods (capture-recapture, multiplier, mapping) with appropriate attention to assumptions and potential biases;

  • Discuss how the above method and other social network-based approaches may provide size

estimations of populations that otherwise remain hidden from routine census efforts.

Background Issues

The epidemiologic and programmatic need to obtain reasonably accurate size estimates of key populations remains strong in the 3rd decade of the HIV epidemic and response. UNAIDS recently supported elucidation of the Network Scale-Up Method which is not yet widely implemented for a variety of reasons. Currently, the Global Fund, UNAIDS and others are working with MEASURE and University of Manitoba to develop a prototype protocol for programmatic mapping and size estimation. New work by Handcock and Gile develops a size estimator based on social network statistics that estimate the size of a network from incomplete network data. (See here for a manuscript.) The estimator can be used in a very straightforward manner by nearly anyone who has implemented a respondent driven sampling survey. Their formula is implemented in the new RDS Analysis tool developed by Handcock, Fellows and others. The field results of this estimator have been analysed by Johnston and others, in comparison with multipliers and capture-recapture results from the same surveys. The estimator should be reviewed independently by the Estimates, Projections and Modelling Reference Group, to get a sense of its validity and how it might be used by surveillance teams globally.

Preliminary Agenda

  • Presentation of the issues with current size estimates
  • Introduction to the size estimator and its construction
  • Review assumptions inherent to the estimator
  • Review results from surveys with multiple size estimations by different methods
  • Review adherence Fto assumptions
  • Presentation and discussion of other potential network-based (e.g., Berchenko) methods
  • Discussion

Colleagues:

If you’ve implemented size estimations with RDS, we would appreciate your preparation of some comparative analyses for the session: Review results from surveys with multiple size estimations by different methods

Background Materials

Software Used in the Presentations

size package for R by Handcock and Gile (source code); Not for redistribution

To install the size package directly use install.packages("size",repos="http://www.stat.ucla.edu/~handcock")

Background Papers

  • [http://arxiv.org/abs/0904.1855 Respondent-Driven Sampling: An Assessment of Current
  • Methodology] by Krista J. Gile and Mark S. Handcock. Pre-print of Sociological
  • Methodology, 40, p 285-327, 2010.

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Notes taken during the workshop

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