The Stats tab of the main window calculates statistics after grouping the animals by date of birth. E.g. this allows you to compute statistics such as the average inbreeding coefficient on a year by year basis, of the number of animals born per decade.
Use of this feature requires that your source data includes the date/year of birth of each animal.
It should also be noted that this feature can use a large amount of memory, particularly if your source data contains a very large number of records. If you do not need this feature you can disable it - use the Compute tab of the Document Settings window (File|Document Settings).
Above the main record table there is a pulldown menu where you specify the date reporting period - you can choose years, decades, months etc. The Period column shows the date range in which animals were born; the Count column holds the number falling in each period.
Above the main record table you will also find an option to restrict the statistics so that only tagged animals are included.
The Report Pane contains several different reports when displaying date period stats: