Table 1. Model definitions* .
| P(MS) | = | The life-time probability of developing MS in the general population.[equated to the prevalence of the disease] |
| (G) , (G–) | = | Sets of persons who either are (G) or are not (G–) genetically susceptible to MS |
| (G1) , (G2) | = | Two mutually exclusive subsets of (G); one consisting of high-penetrance genotypes (G1) and the other consisting of low-penetrance genotypes (G2). (G1) + (G2) = (G) |
| (G0) , (G3) | = | Mutually exclusive sets of genetically susceptible individuals who depend upon (G0) or don’t depend upon (G3) environmental events to get MS. (G0) + (G3) = (G) |
| P(MS|G–) | = | Penetrance of the least penetrant genotype in the population |
| P(MS|Gi) | = | Penetrance of the ith genotype in the set (G) |
| P(MS|G) | = | Expected penetrance of the set (G) ; P(MS|G) = E{P(MS|Gi)} |
| σzi 2 | = | Penetrance Variance within the set (G) ; σzi2 = Var(Gi) |
| P(MS|IGMS) | = | b = the conditional life-time probability of developing a MS, given that the person’s MZ-twin has MS; adjusted to exclude the impact of twins sharing intra-uterine (IU) and childhood (CH) environments. |
| (MZMS) , (DZMS) , (SMS) | = | Sets of persons with a monozygotic (MZ)-twin, a dizygotic (DZ)-twin, or a sibling (S) who either has or will develop MS. |
| (IU) , (CH) | = | Sets of persons who share, with an MS-proband, either the same intra-uterine (IU) or a similar childhood (CH) environment |
| (E) , (E–) | = | Sets of persons who either do (E) or do not (E–) experience a sufficient environmental exposure to produce MS (see Section B) |
| (FT) , (ST) | = | The sets of first (FT) or second (ST) twins of an MZ-twin pair |
| (Gx+) , (Gx–) | = | The set of persons who either possess (Gx+) or don’t possess (Gx–) the particular genetic characteristic (Gx). |
| (HLA+) , (HLA–) | = | The set of persons who either carry (HLA+) or don’t carry (HLA–) at least one HLA DRB1*1501 allele. (HLA+) = (2HB+) + (1HB+) |
| (1HB+) , (2HB+) | = | The sets of persons who carry one (1HB+) or two (2HB+) copies of the DRB1*1501 allele. |
| (1HB–) | = | The set of persons who carry one copy of a non-DRB1*1501 allele ; 
|
| (F) , (M) | = | Sets consisting of either women (F) or men (M) |
| a , a’ | = | P(MS, G) / P(G1) = a ; and: P(MS, G) / P(G2) = a’ |
| b , b’ | = | P(MS|IGMS) = b ; and: P(MS|G, IGMS) = b’ |
| x | = | P(MS|G1) = Expected Penetrance of the high-penetrance subset |
| y | = | P(MS|G2) = Expected Penetrance of the low-penetrance subset |
| z | = | P(MS|G) = Expected Penetrance for the entire set (G) |
| zt , zs | = | P(MS|G, Gx+) = zt ; and: P(MS|G, Gx–) = zs |
| t | = | P(MS|Gx+, IGMS) = P(MS, G|Gx+, IGMS) |
| t’ | = | P(MS|G, Gx+, IGMS) |
| s | = | P(MS|Gx–, IGMS) = P(MS, G|Gx–, IGMS) |
| s’ | = | P(MS|G, Gx–, IGMS) |
| p | = | P(G1|G) = P(G1, G) / P(G) = P(G1) / P(G) ; (G1) ⊂ (G) |
| g | = | P(G|MS) = P(G|IGMS) |
| g1 | = | P(G|Gx+, MS) = P(G|Gx+, IGMS) |
| g2 | = | P(G|Gx–, MS) = P(G|Gx–, IGMS) |
| A0 | = | P(Gx+) |
| A | = | P(Gx+|MS) = P(Gx+|IGMS) |
| MAF | = | Mean allelic frequency – defined as the frequency of an “allelic state”{e.g., the “(HLA–) allele” at the DRB1 gene = one “non-1501” allele} |
| HWE | = | Hardy-Weinberg Equilibrium |
*
See Appendix S1 (Section A) for additional model definitions.