Calculating the reserve for a time and usage indexed warranty

Many products carry a warranty that offers protection for the consumer against low quality. These warranties are often two dimensional, such as an automobile warranty that guarantees repair up to a certain time and mileage after sale. This paper considers the problem of assessing the size of a reserve needed by the manufacturer to meet future claims for such a two-dimensional warranty. To do this, a class of failure models that describe failure by two scales – time and mileage, for example – must be developed. The first half of the paper is devoted to this development. Then the warranty reserve problem is considered in more detail. The problem is described and a decision-theoretic solution, making use of the newly developed reliability model, is proposed.