To avoid the inconsistency issue, it is advisable that in study protocols, study day 0 should not be used. In clinical study protocols, the first day of the study drug administration (or randomization day) should always be counted as day 1 (instead of day 0). With study day 1 being the first day of the study drug administration, the 7 days after treatment will be study day 8, and so on.
1. Studyday calculation ( --DY Variable in SDTM)
2. SAS Programming in the Pharmaceutical Industry