Environmental and heritable factors in the causation of cancer. The genetic epidemiology of cancer: Interpreting family and twin studies Week 4, Stat 246, 2002. Background to and discussion of:
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Environmental and heritable factors in the causation of cancer. The genetic epidemiology of cancer: Interpreting family and twin studiesWeek 4, Stat 246, 2002
Background to and discussion of:
Lichtenstein et al, NEJM343 2000: 78-84, and Risch, Cancer Epi., Biom. & Prev. 10 2001:733-741
Exercise: Obtain the above table and the
corresponding table for full sibs.
For each country (3), sex (2) and zygosity (2), and each of
11 cancer sites or types, Let al have a 22 table of counts.
Here a is the number of concordant affected twin pairs, etc.
Suppose that this table corresponds to DZ twins, say, from
a country where the liability threshold for affectedness is T, and
the components of variance in the bivariate normal model for the
liability are VA (additive),VS (shared environment), and VE
(nonshared environment), all adding to 1. The correlation for DZ
twins’ liabilities is = 0.5 VA +VS , with 1.0 instead of 0.5 for MZ
twins. Their joint analysis of 12 22 tables for a given site or type
assumes country-dependent thresholds, but common,
sex-specific variance components.