Topic Analysis
The Topic Analysis, Rotated SVD option performs a varimax rotation on the partial singular value decomposition (SVD) of the transaction item matrix. See Singular Value Decomposition. You must specify a number of rotated singular vectors, which corresponds to the number topics that you want to retain from the transaction item matrix. After you specify a number of topics, the Topic Analysis report appears.
Topic analysis is equivalent to a rotated principal component analysis (rotated PCA). The varimax rotation takes a set of singular vectors and rotates them to make them point more directly in the coordinate directions (toward the items). This rotation makes the vectors help explain the composition of the transactions as each rotated vector orients toward a set of items. Negative values indicate a repulsion force. The items with negative values occur in a topic less frequently compared to the items with positive values.
Topic Analysis Report
The Topic Analysis report shows the items that have the largest loadings in each topic after rotation. There are additional reports that show the components of the rotated singular value decomposition.
The Top Loadings by Topic report shows a table for each topic. The items in each table are the ones that have the largest loadings in absolute value for each topic. Each table is sorted in descending order by the absolute value of the loading. These tables can be used to determine conceptual themes that correspond to each topic.
The Topic Analysis report also contains the following reports:
Topic Loadings
Contains a matrix of the loadings across topics for each item. This matrix is equivalent to the factor loading matrix in a rotated PCA.
Word Clouds by Topic
Contains a matrix of word clouds, one for each topic.
Topic Scores
Contains a matrix of transaction scores for each topic. Transactions with higher scores in a topic are more likely to be associated with that topic.
Topic Scores Plots
Shows the topic scores for all transactions in one-dimensional scatterplots. Negative values indicate transactions that are negatively associated with a topic. Use these plots to explore the distribution of transactions within each topic.
Variance Explained by Each Topic
Contains a table of the variance explained by each topic. The table also contains columns for the percent and cumulative percent of the variation explained by each topic.
Rotation Matrix
Contains the rotation matrix for the varimax rotation.
Topic Analysis Report Options
The Topic Analysis red triangle menu contains the following options:
Topic Scatterplot Matrix
Shows or hides a scatterplot matrix of the rotated singular value decomposition vectors.
Display Options
Contains options to show or hide content that appears in the Topic Analysis report. See Topic Analysis Report.
Rename Topics
Shows a dialog that enables you to add descriptive names for one or more of the topics.
Save Transaction Topic Vectors
Saves a user-specified number of singular vectors from the rotated singular value decomposition as columns to the data table.
Save Item Topic Vectors
Saves the topic vectors as columns to a new Item Topic Scores data table.
Remove
Removes the Topic Analysis report from the SVD report.