Medical oncologists consider a significant difference in drug clearance to be 15%. Epirubicin's clearance is 84.6 L/h with a standard deviation of 63.5. The researchers have calculated a sample size to have an 80% power to detect a 15% difference. Assuming epirubicin's average clearance is comprised of three separate groups, which is the hypothesis, the researchers would need 29 patients from each genotype to show a 15% difference between the mean clearance of different genotypes assuming a coefficient of variation of 20%. The known polymorphism at amino acid residue 268 has an allele frequency of 50%. This allele was in complete linkage disequilibrium with the new SNP at position -160 in the previous study of morphine. Therefore the researchers would need approximately 120 patients to produce 30 T/T, 60 T/C and 30 C/C.