Syntax

The following statements are available in PROC NESTED.

• PROC NESTED < options > ;

  • CLASS variables < / option > ;

  • VAR variables ;

  • BY variables ;

The PROC NESTED and CLASS statements are required. The BY, CLASS, and VAR statements are described after the PROC NESTED statement.

PROC NESTED Statement

• PROC NESTED < options > ;

The PROC NESTED statement has the following options:

AOV

• displays only the analysis of variance statistics when there is more than one dependent variable. The analysis of covariation statistics are suppressed (see the Analysis of Covariation section on page 2990).

DATA= SAS-data-set

• names the SAS data set to be used by PROC NESTED. By default, the procedure uses the most recently created SAS data set.

BY Statement

• BY variables ;

You can specify a BY statement with PROC NESTED to obtain separate analyses on observations in groups defined by the BY variables. When a BY statement appears, the procedure expects the input data set to be sorted in the order of the BY variables.

Note: When you use the NESTED procedure, your data must be sorted first by the BY variables and, within the BY variables, by the CLASS variables.

If your input data set is not sorted in ascending order, use one of the following alternatives:

• Sort the data using the SORT procedure with a similar BY statement.

• Specify the BY statement option NOTSORTED or DESCENDING in the BY statement for the NESTED procedure. The NOTSORTED option does not mean that the data are unsorted but rather that the data are arranged in groups (according to values of the BY variables) and that these groups are not necessarily in alphabetical or increasing numeric order.

• Create an index on the BY variables using the DATASETS procedure (in base SAS software).

For more information on the BY statement, refer to the discussion in SAS Language Reference: Concepts . For more information on the DATASETS procedure, refer to the discussion in the SAS Procedures Guide .

CLASS Statement

• CLASS variables < / option > ;

You must include a CLASS statement with PROC NESTED specifying the classification variables for the analysis.

Values of a variable in the CLASS statement denote the levels of an effect. The name of that variable is also the name of the corresponding effect. The second effect is assumed to be nested within the first effect, the third effect is assumed to be nested within the second effect, and so on.

By default, class levels are determined from the entire formatted values of the CLASS variables. Note that this represents a slight change from previous releases in the way in which class levels are determined. In releases prior to Version 9, class levels were determined using no more than the first 8 characters of the formatted values, except for numeric variables with no explicit format, for which class levels were determined from the raw numeric values. If you wish to revert to this previous behavior you can use the TRUNCATE option on the CLASS statement. In any case, you can use formats to group values into levels. Refer to the discussion of the FORMAT procedure in the SAS Procedures Guide , and the discussions for the FORMAT statement and SAS formats in SAS Language Reference: Dictionary .

Note: The data set must be sorted by the classification variables in the order that they are given in the CLASS statement. Use PROC SORT to sort the data if they are not already sorted.

You can specify the following option in the CLASS statement after a slash(/):

TRUNCATE

• specifies that class levels should be determined using only up to the first 16 characters of the formatted values of CLASS variables. When formatted values are longer than 16 characters, you can use this option in order to revert to the levels as determined in releases previous to Version 9.

VAR Statement

• VAR variables ;

The VAR statement lists the dependent variables for the analysis. The dependent variables must be numeric variables. If you do not specify a VAR statement, PROC NESTED performs an analysis of variance for all numeric variables in the data set, except those already specified in the CLASS statement.