The multiplicative model is naturally defined for haplotypes as well as genotypes. Indeed, they are equivalent under the assumption of HWE [Sasieni, 1997]. For common diseases we do not expect significant deviations from HWE, and therefore turn to the haplotype setting as a simplifying device for studying genotype models. The same approach has been used by previous authors [Chapman et al., 2003; Pritchard and Przeworski, 2001; Zondervan and Cardon, 2004].
