1. Population Size Estimations With Respondent Driven Sampling
Lisa G. Johnston
Some of these slides are borrowed from University of California, San Francisco, Global Health Sciences 1

2. Outline Multiplier methods^ Wisdom of the Crowds Size-SS
Service multipliers
Unique object multipliers
Wisdom of the Crowds
Size-SS
UNAIDS/WHO Working Group on Global HIV/AIDS and STI Surveillance. (2010) Estimating the Size of Populations Most at Risk to HIV Infection: Participant Manual.

3. Multiplier Method
Two overlapping data sources specific to the population being estimated
Non-duplicated counts of clients or distribution of unique objects
a probability based survey (RDS).

4. Multiplier Assumptions
No individual accounted more than once (non-duplicated data)
Limited in and out migration
Two data sources are independent of each other (i.e., inclusion in one is not related to inclusion in the other)
The survey is representative of the hidden population

5. Multiplier Formula S = N / P S = size of population
N = number of population accessing service/receiving unique object
P = RDS weighted proportion (who reported accessing a service/receiving an object)
If using RDS, you would use the weighted proportion for P. For 95% CI use those generated with the weighted proportions.
Mahy’s comment: consider using a 2x2 table to describe this method.

6. Multiplier example
Estimate the size of the YMSM population. Survey team distributes 400 special key chains to YMSM two weeks before the survey starts.
In the questionnaire, respondents asked if they received a key chain and are shown an example of the object. 10% of the survey respondents reported receiving the key chain.
0.10 = (400/Total YMSM)
Total YMSM = 400/0.1 = 4000
All YMSM
Received
unique
object
YMSM in survey

7. Wisdom of the Crowds-YPWID
“What do you think is the highest of”
“What do you think is the lowest number of”
“What do you think is the most accurate number of”
people 15 to 18 years, living in City X who are injecting illicit drugs?" (please give your best guess)

8. Successive Sampling – Size (SS-Size)
In professional version of RDS Analyst
Assumption that degree is decreasing as sampling progresses
Based on successive sampling
estimator
Need prior PSEs
Need network sizes for each
participant
Recommended: Entry date of
each participants

9. SS-Size Output

10. Thank you!