The affected sib method. II. The intermediate model.

An iteration procedure is outlined which uses HLA haplotype sharing data from sib pairs in which both sibs have the disease of interest. The procedure allows estimation of the degree of dominance of the HLA linked 'disease' allele, and its frequency in the population, for intermediate models where it is assumed that individuals who do not have at least one copy of the 'disease' allele do not contract the disease. Parameter estimates from sib-pair data on multiple sclerosis, insulin dependent diabetes mellitus, haemochromatosis, coeliac disease juvenile rheumatoid arthritis, and Graves' and Hashimoto's diseases are given.