Behavioural Surveillance Surveys - The Wisdom of Whores

sample, it is necessary for the same number
of classes/sections to be chosen from each
sample school, which is another reason for
rounding up to n=40 classes/sections in the
example above. See Chapter 5 for guidance on
the computation and use of sampling weights.
The recommended procedure for selecting
a sample of classes within sample schools is to
first create a list of the classes or sections in
each sample school ordered by grade, and
then select a sample of classes using systematic
sampling with equal probability (since
variations in class sizes within a given school
are likely to be minor, there is little to be
gained by PPS selection). Only grades/levels
in which most students meet the age criteria
for the population survey (e.g., ages 15-19)
should be included in the sampling frames.
Figure 9 provides an example of a systematicrandom
selection of a sample of classes or
sections for a hypothetical school.
Figure 10 : Illustrative example of a systematic-random selection of classes/
sections for a hypothetical secondary school
Grade/Level 3 Selection No. of classes to be sampled = 2
Section 1 Sampling interval = 12/2 = 6
Section 2 Random start = 3
Section 3 X Classes chosen = 3, 9
Section 4
Section 5
Grade/Level 4
Section 1
Section 2
Section 3
Section 4
X
Grade/Level 5
Section 1
Section 2
Section 3
Total classes/sections = 12
Note: grades/levels 1 and 2 not included in sampling frame as, in this hypothetical example,
students in these grades/levels are assumed to be mostly below age 15.
B EHAV I OR A L S U R V EI L L A NC E SURV EY S APPEN DI X 3
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