Behavioural Surveillance Surveys - The Wisdom of Whores

5
Weighting in multi-stage
sampling
This chapter contains key information about analysis for cluster
sampling that will be critical during the planning stage of the survey.
It explains what information must be recorded during data collection so
that appropriate analysis techniques can be applied to adjust for any bias
that may have occurred as a result of the sampling design. Included in this
chapter are 1) a discussion of how multi-stage cluster designs must be
considered in the analysis, 2) instructions on how to calculate sampling
probabilities for weighted analysis and 3) and introduction to cluster analysis.
When and why must the cluster design be
considered for analysis?
Some and perhaps most of the sampling
plans used in the BSS will produce non-selfweighted
samples; that is, samples in which
sub-population members have unequal
probabilities of selection, resulting in potentially
biased samples. The magnitude of the bias will
depend upon two factors: (1) the magnitude of
differences among respondent group members
in terms of probabilities of selection and (2)
the magnitude of differences in behaviors
across sample sites. The standard method
for correcting for unequal probabilities of
selection is to apply sampling weights to the
survey data during analysis, as described below.
B EHAV I OR A L S U R V EI L L A NC E SURV EY S CHAPTER 5
59