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Role
Description
Strata columns
specifies the variables to use to partition the
input table into mutually exclusive,
nonoverlapping subsets that are known as
strata. Each stratum is defined by a set of
values of the strata variables, and each
stratum is sampled separately. The complete
sample is the union of the samples that are
taken from all the strata.
Note: If you do not assign any variables to
this role, then the entire input table is treated
as a single stratum.
You can allocate the total sample size among
the strata in proportion to the size of the
stratum. For example, the variable GENDER
has possible values of M and F, and the
variable VOTED has possible values of Y and
N. If you assign both GENDER and VOTED
to the Strata columns role, then the input
table is partitioned into four strata: males who
voted, males who did not vote, females who
voted, and females who did not vote.
The input table contains 20,000 rows, and the values
are distributed as follows:
n 7,000 males who voted
n 4,000 males who did not vote
n 5,000 females who voted
n 4,000 females who did not vote
Therefore, the proportion of males who voted
is 7,000/20,000=0.35 or 35%. The
proportions in the sample should reflect the
proportions of the strata in the input table. For
example, if your sample table contains 100
observations, then 35% of the values in the
sample must be selected from the males who
voted stratum to reflect the proportions in the
input table.
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Chapter 6 6 / Data Tasks