Behavioural Surveillance Surveys - The Wisdom of Whores

Figure 4 : Example of targeted snowball sampling for the collection of survey
data on IDU
Researchers in San Francisco, California, USA sought to gather data on injecting and sexual
risk-taking behaviors among IDU for use as baseline measures in evaluating behavior change
interventions. The up-front research activities began with an attempt to identify parts of the city
(districts and neighborhoods) that contained high concentrations of IDU and drug-related
activity. To do this, direct observation of neighborhoods were made for signs of drug activity,
key informants (drug treatment program staff, police, and residential hotel desk clerks) were
interviewed, and police arrest records and emergency room admission data were reviewed.
Neighborhoods were then ranked in terms of potential density of IDU, and maps were
developed showing their locations.
In each potential high-activity district, ethnographic mapping exercises were carried out to
identify the predominant “networks” of IDU. This research indicated that although some
sub-groups lived in close proximity to each other, their social interaction was minimal or
non-existent. It was thus necessary to gain entry into several different networks differentiated
along racial, ethnic, and gender lines. Each sub-group was treated as a stratum for sampling
purposes, and a separate quota sample was chosen from each. Paid key informants in each
district/sub-group were used to gain access into the various networks/strata. Snowball sampling
was then used to obtain data for pre-determined sample sizes for each sub-group/stratum.
Source: Watters and Biernacki, 1989
Men who have sex with men (MSM)
Like IDU, men who have sex with men
(MSM) are difficult to enumerate in sample
surveys. However, in many settings MSM
tend to congregate in certain types of
establishments or locations (e.g., certain bars,
nightclubs, parks, neighborhoods, etc.)
in sufficient numbers that such locations
may be used as PSU’s for cluster sampling.
In many settings, this may be the only feasible
means of gathering behavioral data on MSM.
It should be recognized, however, that since
not all MSM frequent such locations, this
approach is prone to bias to the extent that
the behaviors of MSM who frequent such
locations differs from those who don’t.
This potential bias should be borne in mind
when considering survey data on MSM.
The proposed cluster sampling approach
for MSM is quite similar to that used for
floating sex workers. The initial step is the
development of a sampling frame of locations
where MSM congregate. This will require
consultation with key informants and target
group members. In compiling the list of sites,
attention should be paid to ensuring that the
frame covers all geographic parts of the survey
universe and that all relevant “networks” are
included (e.g., MSM of different ethnic or
socio-economic groups).
Once a list of locations has been developed,
time-location sampling units can be created
for use as PSU’s. The list of PSU’s should be
ordered geographically and by type of site
prior to sample selection.
Figure 5 provides an example of cluster
sampling for behavioral surveys of MSM.
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A PPEN DI X 3 B EHAV I OR A L SURV EI L L A NC E S U R V EY S