Survival with competing risks and masked causes of failures

Consider a life testing situation in which systems are subject to failure from independent competing risks. The hazards of various risks are proportional to each other. When a failure occurs, immediate, i.e. stage 1, procedures are used in an attempt to reach a definitive diagnosis. If a diagnosis is not reached, this phenomenon is called masking. Stage 2 procedures, such as failure analysis or autopsy, provide definitive diagnosis for a small sample of the masked cases. This paper shows how stage 1 and stage 2 information can be combined to provide statistical inference about (a) survival functions of the individual risks, (b) the proportions of failures associated with individual risks and (c) probability, for a specified masked case, that each of the masked competing risks is responsible for the failure.