The Consultation considered not only the epidemiology of HIV and other STIs among MSM and transgender

The Consultation considered not only the epidemiology of HIV and other STIs among MSM and transgender
people in different geographical regions, but also reviewed issues associated with the size of the population at
risk, measurement of risk and programmatic responses, and generalizability of the findings.
3.1 Population size estimates
Of key importance, but often not available in many countries, is an estimate of the size of the MSM and transgender
populations. As already noted, the illegality of MSM behaviours in many countries, coupled with social stigma and
widespread discrimination, serve to make MSM behaviours and populations hidden. It is, nonetheless, important
to have estimates of the size of the MSM/transgender populations; it serves not only important purposes as far as
advocacy and human rights are concerned, but also allows those charged with programme planning and priority
setting to make evidence-based decisions, and allocate resources more equitably.
Previous approaches by UNAIDS and others to estimate the size of the MSM/transgender populations in different
settings have relied on literature searches, “best guesses” and cross-sectional surveys. The published literature
yields a generalized figure of 2–4% of the adult male population in many settings where sex with another man is
reported (time frame not specified).
There are several methods for engaging the population of interest, in this case MSM, and estimating the denominator.
These methods include snowball sampling or respondent-driven sampling, capture–recapture, compartmental
methods and others. Methods engaging general populations such as network scale up may provide a more
accurate estimate of population denominator size in some settings. This approach relies upon asking questions to
general population samples about friends and members of their networks. The method has been used to measure
the prevalence of issues such as homelessness, and the incidence of events such as choking in children. It is now
being piloted in some parts of the world to measure reported sexualities; “How many people do you know who are
involved in same-sex relationships?” While there are potential problems related to disclosure (“hidden” behaviours),
network scale up may provide a method of assessing the denominator size in some settings.