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Chapter 12
NestedTerms
Youcan build nested terms for your model in this procedure. Nested terms are useful for modeling
the effect ofa factor or covariate whose values do not interact with the levels of another factor.
Fore xample, a grocerystore chain may follow the spending habits of its customers at several store
locations. Since each customer frequents only one of these locations, the Customer effect can be
said to be nested withinthe Store location effect.
Additionally,you can include interaction effects, such as polynomial terms involving the same
covariate, or add multiple levelsof nesting to the nested term.
Limitations. Nested terms have the following restrictions:
All factors withinan interaction must be unique. Thus, if Ais a factor, thenspecifying A*A
is invalid.
All factors withina nested effect must be unique. Thus, if Ais a factor,then specifying A(A)
is invalid.
No effect can be nested within a covariate. Thus, if Ais a factor and Xis a covariate, then
specifying A(X) is invalid.
Statistics
Figure 12-7
Cox Regression dialog box, Statistics tab