This article describes how to go from a standard table...
...to a table with an additional row that weights the average per row by a specified statistic:
A table with multiple rows and columns.
1. Select your table.
2. In the toolbar go to Automate > Browse Online Library > Table Computations > Weighted Average of Each Column.
3. Change the Statistic to average (if different than the default).
4. Select Statistic to weight by.
5. Press OK.
This rule adds an extra row to the bottom of the table which shows the weighted average of the statistics that are shown in the columns, where they are weighted by the statistic specified in the previous step. Rows which are duplicates of other rows, for example the NET row, are not included in the computation of the average. It is up to the user to ensure that weighting by the chosen statistic makes sense for their analysis.
Note, if you select Switch rows and columns on your table, the rule will no longer work due to the table dimensions changing.