How to Use Breakdown Analysis for Non-Factorial Tables
STATISTICA can calculate descriptive statistics for dependent variables in each of a number of groups defined by one or more grouping, or independent, variables. A breakdown analysis is normally used as an exploratory data analysis technique. The typical question that this technique can help answer is very simple: are the groups created by the independent variables different regarding the dependent variable?
There are two types of breakdown analyses available in STATISTICA: Breakdown & one-way ANOVA and Breakdown; non-factorial tables.
The Breakdown & one-way ANOVA analysis is used to compute various descriptive statistics, correlation matrices, summary graphs, etc., broken down by groups. This option also enables you to perform complete one-way ANOVAs, and provides tests of homogeneity of variance and post-hoc tests of mean differences.
The Breakdown; non-factorial tables analysis is used to compute various descriptive statistics broken down by groups identified by unique combinations of values on the breakdown variables. Unlike the Breakdown & one-way ANOVA analysis, the groups specified in the data do not need to define a full factorial table.
This example is based on a data set reported by Finn (1974). Four groups of 12 subjects each were asked to sort a list of 50 words (each printed on one card) into a specified number of categories. The experimental groups differed with regard to the instructions they received concerning the number of categories represented in the word lists and the actual number of categories in the word lists (as “built” into them by the experimenter).
The data set, Mancova.sta, is one of the example data sets that is included with STATISTICA. To open this spreadsheet, select the File tab. In the left pane, select Open Examples. In the Open a STATISTICA Data File dialog box, double-click on the Datasets folder, select the Mancova.sta file, and click the Open button.
Suppose we want to produce descriptive statistics of how many words were sorted, broken down by GROUP and CATS.
On the Statistics tab in the Base group, click Basic Statistics to display the Basic Statistics and Tables Startup Panel. Select Breakdown & one-way ANOVA.
Click the OK button to display the Statistics by Groups (Breakdown) dialog box.
On the Individual tables tab, click the Variables button. In the variable selection dialog box, select WORDS as the dependent variable, and select GROUP and CATS as the grouping variables. Click the OK button.
In the Statistics by Groups (Breakdown) dialog box, click OK. STATISTICA will automatically choose all codes for the grouping variables, and the Statistics by Groups – Results dialog box will be displayed.
Note that there are numerous options on the Descriptives tab to add various other statistics to the results spreadsheet if desired. For this example, click the Summary button to produce the default descriptive statistics.
Note that this spreadsheet contains results for all group combinations because this analysis assumes the data to be a full factorial design. However, some of the results may not be appropriate to include. Thus, it might be better to consider using Breakdown; non-factorial tables instead, since the data is not a full factorial design.
To do this, resume the analysis by clicking CTRL+R or by clicking the Statistics by Groups button on the analysis bar at the lower-left of the STATISTICA window. In the Statistics by Groups – Results dialog box, click Cancel, and in the Statistics by Groups (Breakdown) dialog box, click Cancel to return to the Basic Statistics and Tables Startup Panel.
Select Breakdown; non-factorial tables.
Click the OK button. In the Statistics BreakDown (non-factorial) dialog box, on the Quick tab, click the Variables button. In the variable selection dialog box, select WORDS as the dependent variable, and select GROUP and CATS as the grouping variables. Click OK.
Note that more statistics can be added to the results spreadsheet via the Descriptives tab. For this example, click the Summary button to produce the default descriptive statistics.
This spreadsheet contains the descriptive statistics for the relevant group combinations given the data. Note that one combination does not have a standard deviation listed, as it only had a sample size of one in this combination of groups.