Computed Categories

In addition to displaying the aggregated results of summary statistics, a table can display one or more categories computed from these aggregated results, from constant values, from subtotals and totals, or a combination of them. The results are known as computed categories or postcomputes. A computed category acts like a category in a single variable with the following similarities and differences:

  • A computed category is positioned like the other categories.
  • A computed category operates on the same statistics as the other categories.
  • Computed categories do not affect subtotals, totals, or significance tests.
  • By default, the values of computed categories use the same formatting for summary statistics as the other categories. You can override the format when defining the computed category.

Because computed categories can be used to total aggregated results, they can be similar to subtotals. However, computed categories have the following advantages over subtotals:

  • Computed categories can be calculated from the results of other subtotals.
  • Computed categories can overlap with each other, operating on the same (or some of the same) categories.
  • Computed categories do not have to include values from all other categories above or below the computed category. That is, computed categories are not exhaustive.
  • Computed categories can include values from categories that are not adjacent.

Unlike totals and subtotals, computed categories are calculated from the aggregated data rather than the original data. Therefore, the values of computed categories may not match the results of totals and subtotals. Also, because you have the option to hide source categories when defining the computed category, it may be difficult to interpret subtotals in the resulting table. If you use computed categories, it is recommended that you specify custom labels for subtotals.

To Define a Computed Category

Computed categories are added from the Categories and Totals dialog box. For information about accessing that dialog box, see the topic Categories and Totals .

  1. In the Categories and Totals dialog box, click Add Category...
  2. In Label for Computed Category, specify a label for the computed category. You can drag categories from the Categories list to include labels for those categories.
  3. Build an expression by selecting categories and/or totals and subtotals and using operators to define the computed categories. You can also type constant values (e.g., 500) to include in the expression.
  4. To show only a computed category and suppress the display of the categories that define the computed category, select Hide categories used in expression from table.
  5. Click the Display Formats tab to change the display format and number of decimal places for the computed category. See the topic Display Formats for Computed Categories for more information.
  6. Click Continue to add the computed category.