Behavioural Surveillance Surveys - The Wisdom of Whores

Floating Sex workers
For sex workers who do not work from
fixed establishments, two alternative sampling
schemes are proposed. The preferred approach
would be to access sex workers at locations
that they frequent, and use a two-stage timelocation
sampling approach, as in Chapter 4.
This approach is illustrated below. The second
approach, recommended for use only if the
preferred approach is not feasible in a given
setting, entails the use of target snowball
sampling, described in Chapter 4.
Time-location cluster sampling
As already mentioned, in some places
it is typical for sex workers to work on a
“freelance” basis, where they are not attached
to any fixed location, but rather come and go
freely from different sites. In this situation,
there is no way to list people at a site, or get
a fixed measure of size for the site. One way
to get around this situation, and still get a
probability sample, is to use the time-location
cluster method introduced in Chapter 4.
In that chapter, the principles used for
developing the sampling frame are described
in detail. A mapping exercise is needed
before a list of time-location clusters can be
developed. The two options for selecting
respondents from PSUs, “take-all” or fixed
number per site are also described in Chapter 4.
The following example illustrates the process
for conducting time-location sampling for
freelance sex workers.
Sampling frame development
In this example, let us suppose that a
mapping exercise has been conducted, using
key informants including sex workers, NGOs
working with sex workers, taxi drivers who
tend to lead men to locations where sex is
sold and some clients of sex workers. Through
the mapping, the team deduces a set of
information about floating sex workers that
they will use to develop the sampling frame.
From the information they have gathered and
the situations they have observed, they will
assume that floating sex workers can be found
in certain bars and hotels, as well as on particular
streets. In addition, they conclude that :
• Friday and Saturday nights are the busiest
nights of the week for floating sex workers,
but some floating sex workers can also be
found during the day.
• There are more floating sex workers at
night than during the day, but those found
during the day on weekdays include
slightly older women, some of whom are
married, but who sell sex during the day
while their husbands are at work.
• If a site is visited twice, on average 20-30%
of the floating sex workers found will be
the same as those who were there on other
days of the week.
• Floating sex workers do not stay in one
place, but tend to circulate among different
sites looking for clients.
• If a site is visited for two hours, on average,
the number of floating sex workers found
will be between 7 and 13, however, some
sites are very large, with as many as 30-40
women, especially on Friday and Saturday
nights after paydays.
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