This article describes how to go from a standard table...
...to a table that adds an asterisk to every cell with a sample size lower than a specified value and a note in the footer indicating the cut-off:
A table with rows and columns.
1. Select your table.
2. Go to Properties > RULES on the object inspector.
3. To apply the rule, select the Plus (+) > Modify Footers > Add a Footnote for Cells with Small Sample Sizes.
4. Set the Minimum Column n that will be used as the threshold (default is 30). Note, if Column Sample Size is not used in the table, Sample Size is used instead.
5. Press OK.