Behavioural Surveillance Surveys - The Wisdom of Whores

Figure 9 : Map of hypothetical sample cluster showing possible starting points
Source : United Nations Children’s Fund. 1995. Monitoring Progress Toward the Goals of the World Summit for
Children : A Practical Handbook for Multiple-Indicator Surveys. New York : UNICEF.
Secondly, when eligible respondents are
identified that for some reason cannot be
easily interviewed (e.g., when they are not at
home), the standard random walk procedure
is to skip such respondents and instead
interview more readily accessible respondents
in other households until the target sample
size or sample quota for the cluster has been
met. As this can cause bias (see below for
further discussion), a different approach is
proposed in the modified version of the
random walk method. The modified procedure
entails following the standard random walk
procedure for identifying the required number
of eligible respondents, but instead of skipping
over respondents who are not readily accessible
for interviewing, making at least three attempts
to interview each eligible respondent identified.
Finally, although the random-walk method
does not call for an actual measure of size to
be obtained for sample clusters, it is proposed
for sub-population surveys that an estimate of
the number of households located in each
cluster be obtained. The reason for this is that
without a measure of size for each sample
cluster, it is impossible to calculate sampling
probabilities, and thus the sample would not
be a probability sample. Note, however, that
obtaining an approximate measure of size for
each cluster does not have to be a costly and
time-consuming activity. In most instances, a
count or rough estimate of the number of
households in a cluster can be obtained from
a knowledgeable local informant. If this is
not possible, a quick tour of the cluster can
usually provide a reasonably accurate count.
This type of “quick count” procedure is often
used in cluster sampling.
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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