Square tables are data tables where the rows and columns have the same labels. These types of tables are also known as switching matrices, transition tables, and confusion matrices. They can all be analyzed using correspondence analysis, but there is a (small) benefit in using a special variant of correspondence analysis designed for such square tables. This article describes how to go from a square table:
To a correspondence analysis output of the square table:
- A square table output which has the same number of rows as columns with identical labels in both the rows and columns which and presented in the same order. For our cereal example above, the rows represent the first brand purchased while the columns represent the second brand purchased.
- Create an output of your square table. For our example, the data was entered using Table > Paste or Enter Data, but you can also create a crosstab from the existing variables in your dataset.
- From the toolbar, select Anything > Advanced Analysis > Dimension Reduction > Correspondence Analysis of a Square Table.
- From the object inspector, select your square table from the Input table dropdown.
- OPTIONAL: Change the Output to show a bubble chart instead of of a scatterplot. When bubble chart is selected, you have the option of selecting an additional variable to represent the Bubble sizes.
- Click the Calculate button to generate the correspondence analysis output.
- Supplementary - A comma-delimited list of labels which are not used to fit the low-dimensional space, but are plotted in the space
- Rows to ignore/Columns to ignore - The names of any rows or columns to be removed from the table prior to analysis
- Horizontal dimension/Vertical dimension - The dimensions to plot on the horizontal and vertical axes respectively. Since dimensions are outputted in order of decreasing variance, the first and second dimensions are usually of most interest.
- Flip horizontally/Flip vertically - Whether to reverse (i.e. invert the sign of) the output coordinates for the specified dimension(s). This may allow better visualization, especially when comparing maps that are similar apart from reflections.
- Use logos for labels - When this option is selected, the user can replace the labels in the scatterplot with logos. The logo should be supplied as a comma-separated list of URLs. See How to Add Images to a Correspondence Analysis Map for more information.
- Maximum number of labels to plot - The option limits the number of labels shown. It is useful when there are many points with overlapping labels. The remaining points will be shown without labels.
- Chart title - Optional title for the scatterplot or bubble chart
- Color - Control the color of the scatterplot points