SPSS Complex Samples⢠13.0 - Docs.is.ed.ac.uk
SPSS Complex Samples⢠13.0 - Docs.is.ed.ac.uk
SPSS Complex Samples⢠13.0 - Docs.is.ed.ac.uk
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7<br />
Sampling from a <strong>Complex</strong> Design<br />
Sampling Wizard: Design Variables<br />
Figure 2-2<br />
Sampling Wizard, Design Variables step<br />
Th<strong>is</strong> step allows you to select stratification and clustering variables and to define input<br />
sample weights. You can also specify a label for the stage.<br />
Stratify By. The cross-classification of stratification variables defines d<strong>is</strong>tinct<br />
subpopulations, or strata. Separate samples are obtain<strong>ed</strong> for e<strong>ac</strong>h stratum. To improve<br />
the prec<strong>is</strong>ion of your estimates, units within strata should be as homogeneous as<br />
possible for the char<strong>ac</strong>ter<strong>is</strong>tics of interest.<br />
Clusters. Cluster variables define groups of observational units, or clusters. Clusters<br />
are useful when directly sampling observational units from the population <strong>is</strong><br />
expensive or impossible; instead, you can sample clusters from the population and<br />
then sample observational units from the select<strong>ed</strong> clusters. However, the use of<br />
clusters can introduce correlations among sampling units, resulting in a loss of
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