All of the summary statistics available for categorical variables are also available for multiple response sets. Some additional statistics are also available for multiple response sets.
E From the menus, choose:
Analyze > Tables > Custom Tables...
E Drag and dropNews sources(this is the descriptive label for the multiple response set$mltnews) from the variable list into the Rows area of the canvas pane.
The icon next to the “variable” in the variable list identifies it as a multiple dichotomy set.
Figure 11-1
Multiple dichotomy set icon
© Copyright SPSS Inc. 1989, 2010 150
Figure 11-2
Multiple dichotomy set displayed in table preview
For a multiple dichotomy set, each “category” is, in fact, a separate variable, and the category labels are the variable labels (or variable names for variables without defined variable labels). In this example, the counts that will be displayed represent the number of cases with aYesresponse for each variable in the set.
E Right-clickNews sourcesin the table preview on the canvas pane and selectCategories and Totalsfrom the pop-up context menu.
E Select (click)Totalin the Categories and Totals dialog box, and then clickApply.
E Right-clickNews sourcesagain and selectSummary Statisticsfrom the pop-up context menu.
E In the Summary Statistics dialog box, selectColumn N %in the Statistics list and click the arrow to add it to the Display list.
E ClickApply to Selection, and then clickOKto create the table.
Figure 11-3
Multiple dichotomy counts and column percentages
Totals That Don’t Add Up
If you look at the numbers in the table, you may notice that there is a fairly large discrepancy between the “totals” and the values that are supposedly being totaled — specifically, the totals appear to be much lower than they should be. This is because the count for each “category” in the table is the number of cases with a value of 1 (aYesresponse) for that variable, and the total number ofYesresponses for allfive variables in the multiple dichotomy set might easily exceed the total number of cases in the datafile.
The total “count,” however, is the total number of cases with aYesresponse for at least one variable in the set, which can never exceed the total number of cases in the datafile. In this example, the total count of 2,081 is almost 800 lower than the total number of cases in the data file. If none of these variables have missing values, this means that almost 800 survey respondents indicated that they don’t get news from any of those sources. The total count is the base for the column percentages; so the column percentages in this example sum to more than the 100%
displayed for the total column percentage.
Totals That Do Add Up
While “count” is typically a fairly unambiguous term, the above example demonstrates how it could be confusing in the context of totals for multiple response sets, for whichresponsesis often the summary statistic you really want.
E Open the table builder (Analyze menu, Tables, Custom Tables).
E Right-clickNews sourcesin the table preview on the canvas pane and selectSummary Statistics from the pop-up context menu.
E In the Summary Statistics dialog box, selectResponsesin the Statistics list and click the arrow to add it to the Display list.
E SelectColumn Responses %in the Statistics list and click the arrow to add it to the Display list.
E ClickApply to Selection, and then clickOKto create the table.
Figure 11-4
Multiple dichotomy responses and column response percentages
For each “category” in the multiple dichotomy set,Responsesis identical toCount—and this will always be the case for multiple dichotomy sets. The totals, however, are very different. The total number of responses is 3,594—over 1,500 more than the total count and over 700 more than the total number of cases in the datafile.
For percentages, the totals forColumn N %andColumn Responses %are both 100%—but the percentages for each category in the multiple dichotomy set are much lower for column response percentages. This is because the percentage base for column response percentages is the total
number of responses, which in this case is 3,594, resulting in much lower percentages than the column percentage base of 2,081.
Percentage Totals Greater Than 100%
Both column percentages and column response percentages yield total percentages of 100%
even though, in our example, the individual values in theColumn N %column clearly sum to greater than 100%. So, what if you want to show percentages based on total count rather than total responses but also want the “total” percentage to accurately reflect the sum of the individual category percentages?
E Open the table builder (Analyze menu, Tables, Custom Tables).
E Right-clickNews sourcesin the table preview on the canvas pane and selectSummary Statistics from the pop-up context menu.
E In the Summary Statistics dialog box, selectColumn Responses % (Base: Count)in the Statistics list and click the arrow to add it to the Display list.
E ClickApply to Selection, and then clickOKto create the table.
Figure 11-5
Column response percentages with count as the percentage base