User’s Guide : Basic Data Analysis : Groups : Descriptive Statistics
  
Descriptive Statistics
These views display the summary statistics of each series in the group. Details for each statistic are provided in “Descriptive Statistics & Tests”.
Common Sample computes the statistics using observations for which there are no missing values in any of the series in the group (casewise deletion of observations).
Individual Samples computes the statistics using all nonmissing observations for each series (listwise deletion).
The two views produce identical results if there are no missing values, or if every series has missing observations for the same set of observations.