TABLE 3.

Linear predictors for genotype variables in a selection of standard disease models.

Genotype	Model
	Multiplicative	Genotypic	Recessive	Dominant
a/a	b 0	b 0	b 0	b 0
a/A	b0 + b1	b0 + b1 + b2	b 0	b0 + b1
A/A	b0 + 2b1	b0 + 2b1	b0 + b1	b0 + b1
Interpretation	b1 provides an estimate of the log odds ratio for disease risk associated with each additional A allele (also called the haplotype relative risk). If b1 is significant, then there is a multiplicative contribution to disease risk in that the odds ratio for disease risk increases multiplicatively for every additional A allele	b1 and b2 provide estimates of the log odds ratio for disease risk in individuals with genotypes a/A and A/A, respectively, relative to an individual with genotype a/a. A likelihood ratio test of whether both b1 and b2 are significant is equivalent to the conventional 2 d.f. test for association in a 2 × 3 contingency table	b1 provides an estimate of the log odds ratio for disease risk in an individual with at least 1 A allele (genotype A/A or a/A) compared with an individual with no A alleles (genotype a/a). A test of whether b1 is significant corresponds to a 1 d.f. test for association in a 2 × 2 contingency table of disease outcome by genotype classified as A/A or not	b1 provides an estimate of the log odds ratio for disease risk in an individual with two A alleles (genotype A/A) compared with an individual with one or two A alleles (genotype a/A or a/a). A test of whether b1 is significant corresponds to a 1 d.f. test for association in a 2 × 2 contingency table of disease outcome by genotype classified as a/a or not