Colony reduction (%) = [(The number of colonies in the presence of pure gelatin -The number of colonies in the presence of gelatin/ZMO)/Number of colonies in the presence of pure gelatin] 100.
โคโลนีลด (%) = [(The number of colonies in the presence of pure gelatin-The number of colonies in the presence of gelatin/ZMO)/จำนวน ของอาณานิคมในต่อหน้าของตุ๋นบริสุทธิ์] 100