specifies a numeric
variable whose values weight the values of the analysis variables.
The values of the variable do not have to be integers. The following
table describes how PROC MEANS treats various values of the WEIGHT
variable.
To exclude observations
that contain negative and zero weights from the analysis, use EXCLNPWGT.
Note that most
SAS/STAT procedures, such as PROC GLM, exclude negative
and zero weights by default.
CAUTION:
Single
extreme weight values can cause inaccurate results.
When one (and only
one) weight value is many orders of magnitude larger than the other
weight values (for example, 49 weight values of 1 and one weight value
of 1×10
^{14}), certain statistics might
not be within acceptable accuracy limits. The affected statistics
are based on the second moment (such as standard deviation, corrected
sum of squares, variance, and standard error of the mean). Under
certain circumstances, no warning is written to the SAS log.
Restrictions:To compute weighted quantiles, use QMETHOD=OS in the
PROC statement.
Skewness and kurtosis are not available with the WEIGHT
statement.
PROC MEANS will not compute MODE when a weight variable
is active. Instead, try using the UNIVARIATE procedure when
MODE needs to be computed and a weight variable is active.
Interaction:If you use the WEIGHT= option in a VAR statement
to specify a weight variable, then PROC MEANS uses this variable instead
to weight those VAR statement variables.
Note:Before Version 7 of SAS, the procedure did not exclude
the observations with missing weights from the count of observations.
Tip:When you use the WEIGHT statement, consider which value
of the VARDEF= option is appropriate.
See the discussion
of VARDEF= and the calculation of weighted statistics in Keywords and Formulas for more information.