You will have to make two decisions here: first, choose a total
number of administrative divisions (clusters) to include in
your sample, and then distribute the clusters between strata.
While budgetary considerations largely dictate the number
of administrative divisions you can sample, every stratum
must be represented. The fewer you choose, the fewer
places your researchers have to visit to conduct interviews,
which translates into lower expenses. However, as a general
rule, the fewer clusters you select, the less representative
your sample of the general population will be.
Generally, aim to select 30-50% of divisions. In countries
with many administrative divisions, the proportion you
select is likely to be smaller. For example, if a country is
divided into 50 divisions, you may only be able to select 15
(30%), whereas in a country with only 10 divisions, you
should easily be able to select five (50%).
Example: In the hypothetical country with 18 states, researchers
should choose nine states (50%).
While proportional representation of each stratum is the
aim when selecting administrative divisions, in most cases
it will not be possible to select an equal proportion from
each stratum.
Example: In the hypothetical example, researchers selected
four out of nine low-conflict states (44%) compared to
three out of five high-intensity states (60%) (see table 2).
Proportional differences at this stage can be rebalanced
when you select the number of sites and interviews.
You will have to make two decisions here: first, choose a totalnumber of administrative divisions (clusters) to include inyour sample, and then distribute the clusters between strata.While budgetary considerations largely dictate the numberof administrative divisions you can sample, every stratummust be represented. The fewer you choose, the fewerplaces your researchers have to visit to conduct interviews,which translates into lower expenses. However, as a generalrule, the fewer clusters you select, the less representativeyour sample of the general population will be.Generally, aim to select 30-50% of divisions. In countrieswith many administrative divisions, the proportion youselect is likely to be smaller. For example, if a country isdivided into 50 divisions, you may only be able to select 15(30%), whereas in a country with only 10 divisions, youshould easily be able to select five (50%).Example: In the hypothetical country with 18 states, researchersshould choose nine states (50%).While proportional representation of each stratum is theaim when selecting administrative divisions, in most casesit will not be possible to select an equal proportion fromeach stratum.Example: In the hypothetical example, researchers selectedfour out of nine low-conflict states (44%) compared tothree out of five high-intensity states (60%) (see table 2).Proportional differences at this stage can be rebalancedwhen you select the number of sites and interviews.
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