However, in the context of studying gene-environment interaction, the assumed genetic model should be taken into account when determining whether the data support a meaningful interaction. That is to say, a three-category genotype cannot be treated agnostically as any three level variable because each category corresponds to a particular genotype. Accordingly, whether an observed interaction is meaningful in a biological sense should be taken into account when evaluating the data. Figure 3 shows the six possible outcomes for the ordering of the genotypic categories and the signs associated with the corresponding slope differences. The signs and significance of A, B and C provide the necessary information to draw conclusions about whether the interaction is likely to be biologically meaningful. We suggest that this information should be taken into account when evaluating statistically significant interaction coefficients, as failure to conform to a likely biological model suggests an increased probability that the interaction is a false positive finding. We provide the framework for this evaluation process in Fig. 3. Note that in the situations represented in Fig. 3c to 3f, whether the
