Behavioural Surveillance Surveys - The Wisdom of Whores

Irrespective of the sampling strategy used,
the guidance provided earlier concerning
numbers of schools and PSU’s also applies to
data collection outside of classes. Choosing
not less than 10-15 schools and 30 or more
“clusters” across sample schools is strongly
recommended. Also note that in order for
a self-weighted sample to result, the same
number of clusters (i.e., either classes/sections
or time-location PSU’s) of equal size should
be chosen in each sample school.
Out of school youth - surveys of youth in the
workplace
In order to obtain behavioral survey data
on out-of-school youth, it will be necessary to
first determine where such youth may be
found. One possibility is to interview youth at
business establishments that typically employ
significant numbers of youth. Examples of
“workplace” sampling frames for youth in
the informal sector would be businesses
employing apprentices, helpers of truck/bus/
van drivers, motorcycle taxi drivers and female
domestic workers.
As the types of businesses/occupations
with significant numbers of youth are likely to
vary from setting to setting, a generic sampling
approach is proposed here. The recommended
approach is a cluster sample design, with
business establishments employing youth
being chosen at the first stage of sample
selection. As with most sub-population
surveys, the sampling frame development
process will begin with consultations with key
informants and members of the population
themselves, the purpose of which is to
determine businesses that employ youth and
the number of youth that are typically found
at such businesses.
Once the sampling frame has been
developed, a sample of workplaces can be
chosen, as was described in Chapter 4, either
with probability proportional to size (PPS) or
with equal probability. PPS selection should
be used when establishments vary significantly
in terms of numbers of youth employees, for
example, if some establishments have 3-4
times as many youth workers as smaller
establishments. Where the numbers of youth
employees associated with establishments are
roughly comparable (i.e., vary in size by a
factor of less than three), sampling with equal
probability will suffice.
If the number of workers who may be
present at sample establishments is likely to
vary from day to day, it is recommended that
time-location cluster sampling be used,
as described in Chapter 4.
Surveys of youth with no fixed residence
(street kids)
For youth that do not have a fixed place of
residence, the sampling approaches described
above for other categories of youth will be
inappropriate. However, a modified cluster
sampling approach in which neighborhoods,
city blocks, public parks, and other locations
where youth with no fixed residence are
known to congregate are used as PSU’s.
This application of cluster sampling methods
is similar to that for floating populations,
described in Chapter 4.
The sampling frame development process
will consist of “up-front” research to determine
the locations within the geographic universe
for the survey where such youth can be
found, the days and times that are the “peak”
and “off-peak” times, and (if possible) the
number of youth that might be expected to be
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