The interaction effect at the marker SNPs decreases quadratically with LD, analogous to the dominance effect. The quadratic factor is a product of the correlation due to each of the tag SNPs. This is again a key result, showing how a simple type of statistical interaction decays with multiple sources of LD, and the relationship later derived for the power to detect the interaction follows directly from it. Crucially, this result contrasts with that for the additive parameter, the decay with LD being quadratic rather than linear.
