highly significantP =1.4×10 −9
Indeed, χ 2 tests for independence revealed that there is a highly significant dependence of APOE genotype and litter across the entire 3-month-old dataset (χ 2 =82.7, d.f.=20, P =1.4×10 −9 ), as well as within only male samples (χ 2 =43.1, d.f.=14, P =8.2×10 −5 ) and within only female samples (χ 2 =39.3, d.f.=14, P =3.0×10 −4 ).