The most parsimonious model of the contribution of MAOA genotype to risk for CD included only additive effects (Table 2, model 2, deviance = 372.6, AIC = 374.6). MAOA was subsequently modeled in an additive fashion (low activity = 1, low/high activity = 0 and high activity=−1) because (1) dominance effects were not significant within the additive/dominance model, (2) improvement in model fit was observed for the more parsimonious additive model and (3) a model of dominance in the direction of high activity (model 4) seemed to oversimplify the effect of the heterozygotes.
