The proportional hazards assumption may not be realistic for all
data. If so, it may still be reasonable to perform a
stratified analysis. The STRATA statement names the variables
that determine the stratification.
Strata are formed according to the nonmissing values of the STRATA
variables unless the MISSING option is specified.
In the STRATA statement, variable is a variable with
values that are
used to determine the strata levels, and list is an optional
list of values for a numeric variable. Multiple variables can appear
in the STRATA statement.
- STRATA variable < ( list ) > < ... variable <
( list ) >> < /option > ;
The values for variable can be formatted or unformatted. If the
variable is a character variable, or if the variable is numeric and no
then the strata are defined by the unique values of the variable.
If the variable is numeric and is followed by a list, then the levels
for that variable correspond to the intervals defined by the list.
strata are formed by the combination of levels and unique values.
The list can include numeric values separated by commas or blanks,
value to value by value range specifications,
or combinations of these.
For example, the specification
strata age (5, 10 to 40 by 10) sex ;
indicates that the levels for age are to be less
than 5, 5 to 10,
10 to 20, 20 to 30, 30 to 40, and greater than 40.
(Note that observations with
exactly the cutpoint value fall into the interval above the cutpoint.)
Thus, with the sex variable, this STRATA statement specifies 12
The following option can be specified in the STRATA statement
after a slash (/).
allows missing values (`.' for numeric variables and blanks
for character variables) as valid STRATA variable values.
Otherwise, observations with missing STRATA variable values are deleted
from the analysis.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.