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Chapter 1
Unequalselection probabilities. When sampling clusters that containunequal numbers of units,
you can use probability-proportional-to-size(PPS) sampling to make a cluster’s selection
probability equal to the proportion of units it contains. PPS sampling can also use more general
weighting schemes to select units.
Unrestrictedsampling. Unrestricted sampling selects units with replacement (WR). Thus, an
individual unit can be selected for the sample more than once.
Sampling weights. Sampling weights are automatically computed while drawing a complex
sample and ideallycorrespond to the “frequency” that each sampling unit represents in the target
population. Therefore, the sum of the weights over the sample should estimate the population
size. Complex Samples analysis procedures require sampling weights in order to properly analyze
a complex sample. Note that these weights shouldbeusedentirelywithintheComplexSamples
option and shouldnot be used with other analytical procedures via the Weight Cases procedure,
which treats weights as case replications.
Usage of Complex Samples Procedures
Yourusage of Complex Samples procedures depends on your particular needs. Theprimary
types of users are those who:
Plan andcarry out surveys according to complex designs, possibly analyzing the sample later.
The primary tool for surveyors is the Sampling Wizard.
Analyzesample data file s previously obtained according to complex designs. Before using the
Complex Samples analysis procedures, youmay need to use the Analysis Preparation Wizard.
Regardless of which type of user you are, you need to supply design information to Complex
Samples procedures. This information is stored in a plan file for easy reuse.

Plan Files

Aplanfilecontains complex sample specifications. Thereare two types of plan files:
Sampling plan. The specifications given in the Sampling Wizard defineasampledesignthat
is used to draw a complex sample. The sampling plan file contains those specifications. The
sampling planfile also containsa default analysis plan that uses estimation methods suitable for
the specified sample design.
Analysisplan. Thisplan file contains information needed by Complex Samples analysis procedures
to properly compute variance estimates for a complex sample. The plan includes the sample
structure, estimationmethods for each stage, and references to required variables, such as sample
weights. The Analysis Preparation Wizard allows you to create and edit analysis plans.
There are several advantages to saving your specificationsin a plan file, including:
A surveyor can specify the first stage of a multistage sampling plan and draw first-stage
units now,collect information on sampling units for the second stage, and then modify the
sampling plan to includethe second stage.