It gives me an error saying my parameter field cannot be summarized. Here's the code...
if minimum({?PERIOD}) in cdate(2006,12,27) to cdate(2007,1,23) then "Period 1" else
if minimum({?PERIOD}) in cdate(2007,1,24) to cdate(2007,2,20) then "Period 2" else
if minimum({?PERIOD}) in...