By default, when you carry out a column proportions, column mean, net difference test, or paired preference test, if a table includes a base value that is below the recommended minimum base of 30, the test is not carried out. This is denoted by two asterisks (**), which are placed on the table instead of the result. If a table includes a base value that is above the minimum base but below a "small base" value of 100, the test is carried out, but a single asterisk (*) next to the test denotes that the base value is small. The annotations also indicate this.
You can change the default minimum base and small base values if required, by entering new values in the Minimum Base and Small Base fields in the Statistics tab of the Table Properties dialog box.