BSSR Resources, Methods, and Measures

Estimating the Size of Hard-to-count and Uncountable Populations

Systematic research on methods for estimating hard-to-count populations is needed in order to better guide public health policy. How many civilians died a war zone [Syria, Afghanistan, Libya, Yemen]? How many women were raped last year in [India, Mexico, Nigeria, the U.S....]? Methods in current use for estimating these populations include the capture-recapture, multiplier, respondent-driven sampling and network scale-up (NSUM) methods. All of these methods have advantages and disadvantages and all can be improved with systematic research. NSUM has been used by researchers from UNAIDS in various countries to estimate the number of MSM (men who have sex with men) and other populations at risk for HIV. It has been used in Brazil, Japan, Iran, Ukraine, Thailand, China and other countries to estimate other hard-to-count populations, like the number of women having abortions, injecting drug users, and sex workers and their clients. The network scale-up method was developed by researchers at the University of Florida with support from the Methodology, Measurement, and Statistics program of the U.S. National Science Foundation (, The method is being improved (made increasingly accurate) by a new generation of researchers ( With appropriate funding we can improve the accuracy of all methods for estimating the size of hard-to-count populations.

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Idea No. 328