# Weight cases

Weight Cases gives cases different weights (by simulated replication) for statistical analysis.

- The values of the weighting variable should indicate the number of observations represented by single cases in your data file.
- Cases with zero, negative, or missing values for the weighting variable are excluded from analysis.
- Fractional values are valid and some procedures, such as Frequencies, Crosstabs, and Custom Tables, will use fractional weight values. However, most procedures treat the weighting variable as a replication weight and will simply round fractional weights to the nearest integer. Some procedures ignore the weighting variable completely, and this limitation is noted in the procedure-specific documentation.

Once you apply a weight variable, it remains in effect until you select another weight variable or turn off weighting. If you save a weighted data file, weighting information is saved with the data file. You can turn off weighting at any time, even after the file has been saved in weighted form.

**Weights in Crosstabs. **The Crosstabs procedure has several
options for handling case weights. See the topic Crosstabs cell display for more
information.

**Weights in scatterplots and histograms.** Scatterplots and
histograms have an option for turning case weights on and off, but
this does not affect cases with a zero, negative, or missing value
for the weight variable. These cases remain excluded from the chart
even if you turn weighting off from within the chart.

To Weight Cases

- From the menus choose:
- Select Weight cases by.
- Select a frequency variable.

The values of the frequency variable are used as case weights. For example, a case with a value of 3 for the frequency variable will represent three cases in the weighted data file.