Behavioural Surveillance Surveys - The Wisdom of Whores

Fieldwork assignments when the “take-all”
strategy is used to select sample target group
members
A key aspect of the proposed sampling
strategy is that sample PSU’s or clusters be
visited for the same amount of time and that
all target group members who appear at the
site during the period chosen for data collection
be included in the sample. For sites where
relatively small numbers of sex workers are
expected, it may be feasible for a single
interviewer to “capture” all sex workers
appearing at the site. However, where the
expected number of respondents is larger,
it would be advisable to deploy a sufficient
number of interviewers to ensure that all sex
workers appearing at the site are interviewed.
The failure to do so may result in the sample
size target for the group not being met, as well
as possibly causing bias.
Although the “take-all” strategy results in
a self-weighted sample, it is a good idea to
record all the same information outlined in
Table 1. That way, if mid-way through the
survey it is found that continuation of the
strategy is not possible because the interviewers
are unable to interview all respondents at the
site, it will still be possible to correct a non
self-weighted sample at the time of analysis.
How to handle duplicates with time-location
sampling
If a respondent who is interviewed as part
of one time-location cluster is encountered
again in another time-location cluster, that
person should not be interviewed a second
time, but rather recorded as a duplicate.
However, it is possible that a respondent may
refuse to be interviewed in one time-location
cluster, but then accept to be interviewed in
another. In that case, that respondent should
not be counted as a duplicate, but rather as a
refusal in the first cluster, and a completed
interview in the second cluster
Targeted snowball sampling
approach
In some settings, floating sex workers may
not congregate in public places, and thus the
cluster sampling approach described above
will not be feasible. For example, in some
places, encounters with sex workers are
sometimes arranged through “brokers”, or
arrangements are made via telephone. If a
significant portion of the commercial sex trade
operates in this fashion in a given setting,
then probability sampling methods will not be
feasible and the targeted snowball sampling
approach described in Chapter 4 will become
the next best option.
As described earlier, the key aspect of
targeted snowball sampling is to determine
which networks exist in a given setting.
In the case of sex workers, this may entail
determining who the major brokers or
controllers of sex workers are, gaining
entrance into the network, and using snowball
sampling techniques to identify target group
members in each network.
320
A PPEN DI X 3 B EHAV I OR A L SURV EI L L A NC E S U R V EY S