Suppose we wish to investigate the familial aggregation of respiratory disease according to the specific type of respiratory disease. One hundred families in which the head of household or the spouse has asthma, referred to as type 1 families, and 200 families in which either the head of household or the spouse has non-asthmatic pulmonary disease, but neither has asthma, referred to as type B families, are identified. Suppose that in 15 of the type 1 families the first-born child has asthma, whereas in 3 other type 1 families the first-born child has some nonasthmatic respiratory disease. Furthermore, in 4 of the type B households the first-born child has asthma, whereas in 2 other type B households the first-born child has some nonasthmatic respiratory disease.