The following attachement has tips about dealing with missing data. In summary,missing data entered as blank cells in Phoenix will perform better than any other representation, Phoenix has tools to perform data manipulations on blank (ie., null) data cells and the user can still import/export these cells with a different representation if desired. See attachment for details and screenshots [file name=Tip___blanks.docx size=370102]http://pharsight.best.vwh.net/extranet/media/kunena/attachments/legacy/files/Tip___blanks.docx[/file][Tip___blanks.docx|attachment](upload://ozRozuLmK99zqdH7gWX6TaKqX6U.docx) (361 KB)