The allele frequency of 3R tandem repeats is 0.6 and 2R tandem repeats is 0.417. In 100 patients therefore, one would expect 16 patients with 2R/2R genotypes, 48 with 2R/3R genotypes and 36 with 3R/3R genotypes. It is interesting to note that the incidence of grade 3/4 palmar plantar erythrodysesthesia and diarrhea is on the order of 14 to 16 percent. A sample of 104 patients would have a power of 0.8 to show a statistically significant difference of 40% between 2R/2R (60 %) and 3R/3R (20 %).