• marginal models;
  • copula models;
  • sibling recurrence risk;
  • present state data


The relative recurrence risk ratio λR (and particularly the sibling recurrence risk ratio, λS ) is often of interest to those wanting to quantify the genetic contribution towards risk of disease or to discriminate between different genetic models. However, estimating λR for complex diseases for which genetic and environmental risk factors are both involved is not straightforward. Ignoring environmental factors may lead to inflated estimates of λR. We present a marginal model which uses a copula function to model the association in cumulative incidence rates between pairs of relatives. This model is applicable to present-state data and allows estimation of risk of disease in a pair of relatives (and hence λR), given measured environmental covariates. We apply the model to leprosy among sibling pairs from the Karonga district, Malawi. If risk factors are ignored, the apparent λS in this population is over 3. Accounting for known nongenetic risk factors reduces it to just under 2. Genet Epidemiol 25:293–302, 2003. © 2003 Wiley-Liss, Inc.