2.1 Introduction

Development of any product involves designing processes that can result in the desired product. Successful development of a product depends on the effectiveness of the underlying processes. Naturally, process variability is a concern for any product development team, since it affects the reliability and quality of the product. To manage the processes, we have to measure it, especially the variations and the uncertainties associated with them. Apart from various other factors, market success of a product would depend on how the company manages to meet the customer requirements under uncertainties. For example, customers may be happy with a courier company which delivers documents with mean duration of two days and standard deviation of one day compared to another company which delivers the documents with mean duration of one day with standard deviation of two days. In the first case, the probability that a document will not be delivered within 4 days is approximately 2.27% (assuming normal distribution), whereas the same probability is 6.67% in case of second company, although its average time to deliver the document is one day. Similarly, a customer purchasing a product such as consumer durables would expect the product to function properly to begin with and maintain the functionality for a minimum duration. This 'minimum duration' is subjective and would vary from product to product. Here, there are two uncertainties; one corresponds to the probability that a newly...