This article describes how to go from a table with spans...
...to a table that includes an Average row per span:
A table that includes grouped spans in the question that is displayed in the rows.
1. Select your table.
2. Go to Properties > RULES on the object inspector.
3. To apply the rule, select the Plus (+) > Browse Online Library > Table Computations > Add Average Rows to Tables Containing Spans > OK.
This rule adds an Average column to the right of every span which is computed as the average of the statistics of the other columns within that span. No significance tests are conducted on these averages.
Note, if you select Switch rows and columns on your table, the rule will no longer work due to the table dimensions changing. In this case, you will have to apply the Add Average Columns to Tables Containing Spans rule instead.