Behavioural Surveillance Surveys - The Wisdom of Whores

Figure 3 : Decision tree for first- and second-stage cluster sampling approaches
Yes
Are the target members
accessible at a physical site?
No
Are target group members associated
with sites in a fixed manner, or do
they come and go freely?
Snowball sampling
Associated with site in
fixed manner
Come and go freely
from site
Is it possible to get an
estimated MOS for site?
Use time location
cluster sampling
Is average number of target
group members during a fixed time
interval small (i.e. 15 or fewer)
Yes
No
Yes
No
1 st stage :
select clusters
with probability
proportional to
size (PPS)
Note : SW
NSW
MOS
2 nd stage :
Select equal
number of
respondents
from each
cluster (SW)
= self-weighted
= non self-weighted
= measure of size
1 st stage :
Select clusters
by equal
probability (EP)
2 nd stage :
Subsample
fixed number
from each
cluster (NSW)
1 st stage :
Select time
location clusters
with equal
probability (EP)
2 nd stage :
“take-all”
for each cluster
during equal
time period
(SW)
1 st stage:
Select time
location clusters
by equal
probability (EP)
2 nd stage:
subsample fixed
number from
each cluster
during equal
time period for
each cluster
(NSW)
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C H A PTER 4 B EHAV I OR A L S U R V EI L L A NC E S U R V EY S