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Fifty patients with severe aplastic anemia had no transfusions of blood products until just before marrow transplantation from HLA-identical family members. Of the 50, 42 are still alive 1 to 12 years after transplantation (median, 7 years). By actuarial standards, the 10-year probability of survival is 82%. Of the 42 surviving patients, 37 have Karnofsky performance status scores of 100% and 5 with chronic graft-versus-host disease have scores ranging from 50% to 90% (median, 80%). The 8 deaths were caused by early infection in 1, graft rejection in 1, acute graft-versus-host disease in 3, and chronic graft-versus-host disease in 3. All deaths occurred within two years after transplantation. The incidence of graft failure was 10%. Acute graft-versus-host disease developed in 14 of 44 patients at risk and chronic graft-versus-host disease, in 15 of 41. Risk factors for development of chronic graft-versus-host disease included increased age (p = 0.008) and presence of acute graft-versus-host disease (p = 0.001). The only factor associated with increased risk of death was development of acute graft-versus-host disease (p = 0.05). Results of this study extend our previous finding that patients with severe aplastic anemia who have transplants before the onset of transfusion-induced sensitization have an excellent probability of long-term survival and a normal life.

Distinct problems in the analysis of failure times with competing causes of failure include the estimation of treatment or exposure effects on specific failure types, the study of interrelations among failure types, and the estimation of failure rates for some causes given the removal of certain other failure types. The usual formation of these problems is in terms of conceptual or latent failure times for each failure type. This approach is criticized on the basis of unwarranted assumptions, lack of physical interpretation and identifiability problems. An alternative approach utilizing cause-specific hazard functions for observable quantities, including time-dependent covariates, is proposed. Cause-specific hazard functions are shown to be the basic estimable quantities in the competing risks framework. A method, involving the estimation of parameters that relate time-dependent risk indicators for some causes to cause-specific hazard functions for other causes, is proposed for the study of interrelations among failure types. Further, it is argued that the problem of estimation of failure rates under the removal of certain causes is not well posed until a mechanism for cause removal is specified. Following such a specification, one will sometimes be in a position to make sensible extrapolations from available data to situations involving cause removal. A clinical program in bone marrow transplantation for leukemia provides a setting for discussion and illustration of each of these ideas. Failure due to censoring in a survivorship study leads to further discussion.

A model is proposed for the study of plant breeding where the self-fertilization rate is of importance. The model can be used to provide convenient maximum likelihood estimation of the self-fertilization rate and allelic frequencies in a parental population and its pollen pool. The self-fertilization rate can also be allowed to vary with genotype or other characteristics of a plant. A simple example illustrates the methodology.

When a number of families can be identified with two or more siblings having a particular disease, Green & Woodrow proposed a test for MHC-disease association. An extension of this test is presented to detect more general associations when family sizes exceed three.