Analytical and graphical methods to model the association between family history and disease from a case-control study

Subjects within a family have a high probability of sharing environmental f actors as well as genes. Without any previous hypothesis, familial aggregat ion cannot be attributed to genetic or environmental factors. In epidemiolo gy a common measure of familial aggregation is the odds ratio (OR) evaluate d from case-control studies which gives a measure of the increased risk ass ociated with particular aspects of the family's history of disease. An anal ytical method is presented to model the OR of case-control studies in the p resence of risk factors, genetic or environmental, that are correlated betw een relatives. A graphical approach that can be used to link the parameters of the model with the values of the OR is also described. The method is il lustrated using the example of familial aggregation in colorectal cancer.