Fig. 3
Conformity of the observed effect of combining different MHC haplotypes with an additive and a multiplicative model of combined risk. Yellow bands represent the definitional odds ratios (ORs) relative to a reference group consisting of the (AP,AP) or (AP*) genotype (i.e., as defined in the text: Rb = RAP* = 1). With the exception of (c1), which seems to behave in a unusual fashion, the combination of other risk alleles produced, in general, a risk in between the two models, albeit closer to that predicted by the additive model. All combinations had, at least, 50 representations in the WTCCC and the green shading indicates the ORs actually observed. Cells with yellow shading in the “Observed” column also represents the ORs actually observed. However, in these yellow-highlighted cases, the ORs were used to approximate the relative risks (RRs), which, in turn, were used to assess whether the genotypes that are not yellow-highlighted conformed to the additive and multiplicative models (see “Methods” section)