I have been using the combination index chou Talalay method to evaluate THE EFFICACY OF A DRUG COMBINATION ( Vitamin D and Cisplatin ) actualy the vitamin D by its self is not cytotoxic to the cells it just has an enhancing effect on the cytotoxic drug . so when I try feeding the data to the programe first the program doesnt accept values for Fa more than 1 which is actualy the case because certain doses of vitamin D increases the proloferation of the cancer cells . The graphs looks very strange and the datas ( CI values are some times not indicative) If any one has experience with that situation please help .