In the Contingency platform, the Correspondence Analysis option provides a graphical technique to visualize which rows or columns of a frequency table have similar patterns of counts. In the correspondence analysis plot, there is a point for each row and for each column. Use Correspondence Analysis when you have many levels, which might make it difficult to derive useful information from the mosaic plot. See Example of Correspondence Analysis.
Correspondence Analysis plots contain row and column profiles. The row profile can be defined as the set of rowwise rates, or in other words, the counts in a row divided by the total count for that row. If two rows have very similar row profiles, their points in the correspondence analysis plot are close together. Squared distances between row points are approximately proportional to chi-square test statistics that test the homogeneity between the pair of rows.
Column and row profiles are alike because the problem is defined symmetrically. The distance between a row point and a column point has no meaning. However, the directions of columns and rows from the origin are meaningful, and the relationships between the points can help you interpret the plot.
Use the options in the Correspondence Analysis red triangle menu to add a three-dimensional scatterplot to the Contingency report and to add column properties to the data table.
3D Correspondence Analysis
Shows or hides a three-dimensional scatterplot.
Save Value Order
Saves a Value Ordering column property to both the X and Y variable columns in the data table. The column property specifies the order of the levels sorted by the first correspondence score coefficient.
In the Contingency platform, the Details report contains statistical information about the correspondence analysis and shows the values used in the plot.
Singular Value
The singular value decomposition of the contingency table. See Statistical Details for Correspondence Analysis.
Inertia
The square of the singular values, reflecting the relative variation accounted for in the canonical dimensions.
Portion
The portion of inertia with respect to the total inertia.
Cumulative
The cumulative portion of inertia.
Tip: If the first two singular values capture the bulk of the inertia, then the 2-D correspondence analysis plot is sufficient to show the relationships in the table.
X Variable c1, c2, c3
The values plotted on the Correspondence Analysis plot.
Y Variable c1, c2, c3
The values plotted on the Correspondence Analysis plot.