To determine whether allogeneic bone-marrow transplantation is associated with a graft-versus-leukemia effect, we examined the relation between relapse of leukemia and graft-versus-host disease in 46 recipients of identical-twin (syngeneic) marrow, 117 recipients of HLA-identical-sibling (allogeneic) marrow with no or minimal graft-versus-host disease, and 79 recipients of allogeneic marrow with moderate to severe or chronic disease. The relative relapse rate was 2.5 times less in allogeneic-marrow recipients with graft-versus-host disease than in recipients without it (P less than 0.01). This apparent antileukemic effect was more marked in patients with lymphoblastic than nonlymphoblastic leukemia, and in those who received transplants during relapse rather than during remission, and was most evident during the first 130 days after transplantation. Survival of all patients was comparable since the lesser probability of recurrent leukemia in patients with graft-versus-host disease was offset by a greater probability of other causes of death.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Biometrika Trust is collaborating with JSTOR to digitize, preserve and extend access to Biometrika. SUMMARY Estimation in Cox's failure time regression model is considered when the regression vector is subject to measurement error. A hazard function model is induced for the failure rate given the measured covariate and a partial likelihood function is derived for the relative risk parameters. This partial likelihood function may involve the baseline hazard function as well as the regression parameter, but useful inference techniques arise for testing whether the regression parameter equals zero and for more general inferences in important special cases. Explicit consideration is given to testing equality of survival curves when group membership is subject to misclassification and to relative risk estimation with normally distributed covariates. Approaches to regression estimation using the overall likelihood function, and a marginal likelihood function based on failure time ranks, are also indicated. Illustration of the possible effect of covariate errors on relative risk estimation is provided.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Biometrika Trust is collaborating with JSTOR to digitize, preserve and extend access to Biometrika. SUMMARYSuppose that a cohort of individuals is to be followed in order to relate failure rates to preceding covariate histories. A design is proposed which involves covariate data only for cases experiencing failure and for members of a randomly selected subcohort. Odds ratio and relative risk estimation procedures are presented for such a 'case-cohort' design. A small simulation study compares case-cohort relative risk estimation procedures to full-cohort and synthetic case-control analyses. Relevance to epidemiologic cohort studies and disease prevention trials is discussed.

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