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Population Size Estimation of Key Populations and HIV Prevention Cascades

April 12, 2021 - April 15, 2021

Establishing the size of various populations at risk for HIV has been identified as one of the greatest challenges in HIV surveillance and in developing estimates of HIV prevalence and incidence. Reliable estimates of the size of populations at high risk for HIV are important for prioritizing target populations, planning HIV prevention services, measuring coverage with these services and monitoring and evaluation of interventions. 

The aim of the course is to provide participants with practical guidance on how to design studies to estimate the size of key populations (female sex workers [FSW], people who inject drugs [PWID], men who have sex with men [MSM]) and transgender persons), conduct these studies, and analyze, interpret and use the data. The course will  outline the approaches that can be used for extrapolating local data to develop national size estimates by applying various adjustments. 

Presentations will reflect on design and implementation of virtual mapping of internet sites and various phone-based applications, which is emerging new approach in population size estimation.  

The course will also address HIV prevention cascade, including PrEP cascades, and provide examples of various models for constructing those cascades. They can be made using integrated HIV bio-behavioural surveys in key populations, population size estimation and routine programme data.  

Lectures will be followed by discussions about case studies to enable interactive exchange of knowledge and experiences.

Key topics of the course are: 

  • Methods used to estimate the size of KPs: mapping (including mapping of virtual platforms); multiplier method; capture-recapture; network scale-up   
  • Circumstances when it is appropriate to use specific size estimation methods 
  • Potential for under and over-estimation  of PSE methods 
  • Extrapolation from local size estimation to sub-nation and national estimates using extrapolation procedures  
  • Data quality challenges in PSE studies 
  • Framework for HIV prevention cascade
  • Challenges in constructing HIV prevention cascade such as determining the initial denominator, time covered by the cascade, multiple prevention options and final outcome
  • Use of HIV prevention cascades as management tools that identify gaps and related barriers and advocacy tools for indicating points for intervention to enhance programme effectiveness

Objectives of the course are the following:

  • To illustrate methods used to estimate the size of KPs at higher risk of HIV
  • To describe approaches used to extrapolate data from areas with local population size estimates to the sub-national and national level 
  • To build skills in field procedures for size estimation studies   
  • To learn how to use multiple data sources for KP programme improvement, including HIV care cascade analysis

Participants will be given opportunities to share their own country-specific experiences and challenges in estimating the size of KPs.  

Key aspects of the course is a group/individual work. Participants can choose between these options:

  1. To develop a protocol for a size estimation study 
  2. To make a proposal for HIV prevention cascades that might be used in participants’ countries  

Participants will present the results of this work on the final day of the course.  

Teaching Methods

The course consists of lectures, presentation of case studies, active class discussion, exercises and group work. The course is designed to provide participants with practical skills and knowledge on how to conduct size estimation studies. 

Target Audience

Epidemiologists, demographers, public health professionals, social scientists

Course fee

Course fee is 1000 USD and includes all course materials.


Ivana Bozicevic, MD, DrPH, WHO Collaborating Centre for HIV Strategic Information, School of Medicine, University of Zagreb, Croatia

Jurja Ivana Adamsky, MD, WHO Collaborating Centre for HIV Strategic Information, School of Medicine, University of Zagreb, Croatia

Zoran Dominkovic, WHO Collaborating Centre for HIV Strategic Information, School of Medicine, University of Zagreb, Croatia



12 April 2021
9.00-9.30 Welcome 
9.30-10.00 Introduction to population size estimation (PSE): Overview of why and how  
10.00-10.45 Discussion with participants about challenges with PSE in their settings
10.45-11.00 Break 
11.00-11.30 Multiplier method
11.30-12.15 Case study: multiplier method
12.15-14.00 Lunch break
14.00-14.30 Capture-recapture
14.30-15.15 Case study: capture-recapture
15.15-16.00 Methods based on data collected from the general population: 

Adding direct questions to population based surveys 

Network scale-up

16.00-16.20 Discussion about network scale-up
13 April 2021
9.00-9.45 Geographical mapping and enumeration
9.45-10.30 Virtual mapping of internet sites and various phone-based applications
10.30-10.45 Break
10.45-11.15 Discussion about mapping (circumstances when it is appropriate do to, advantages and disadvantages)
11.15-12.00 Case study: mapping
12.00-14.00 Lunch break
14.00-14.40 Triangulation of results of various size estimation methods with examples 
14.40-15.20 Constructing national estimates step-by-step 

Data extrapolation procedure

15.20-15.30  Break
15.30- 16.20 Case study: constructing national size estimates 
14 March 2019
9.00-9.30 Using size estimation data to estimate programme coverage 

Frameworks for HIV prevention cascade 

10.15-10.30 Break
10.30-11.15   Using HIV prevention cascade for identifying missed opportunities in PrEP delivery 
11.15 – 12.00 Examples of constructing HIV prevention cascades for KPs using various data sources
12.00-12.30 PMTCT  cascade
12.30-14.00 Lunch 
14.00-14.20 Introduction to group or individual work supported by facilitators
14.20-16.00  Work on the proposals/ protocols
15 April 2021
9.00-9.45 Discussion: Feasibility of constructing HIV prevention cascades in the countries 

Data availability and quality challenges 

9.45-10.30  HIV recent infection surveillance as a tool to better understand targets for primary prevention 
10.30-10.45 Break 
10.45-12.30 Work on the proposals/ protocols
14.00-16.15 Presentations of group/ individual work 


April 12, 2021
April 15, 2021


Online Training Course


HIV Evaluation Center

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