Robust design requirements specification: a quantitative method for requirements development using quality loss functions

Product requirements serve many purposes in the product development process. Most importantly, they are meant to capture and facilitate product goals and acceptance criteria, as defined by stakeholders. Accurately communicating stakeholder goals and acceptance criteria can be challenging and more often than not, requirements will be subject to simplification, causing ambiguity and uncertainty, with negative consequences for the company and the users. To prevent such incidences, a new approach for creating more complete requirements is proposed in this article. Grounded in robust design theory, the approach uses quality loss functions as one of the five principles, to visualise a more complete set of requirement information in a single figure. In order to validate the potential and applicability of the proposed approach, a new indicator for requirement completeness is introduced, expressing how open the requirements are for interpretation. By applying the method and indicator to a case study from the medical device industry, it was found that less than 45% of the potential for quantification had been utilised. Finally, the robust design requirements specification method was successfully applied to three case study requirements, to illustrate the gains in terms of the level of quantification, transparency, and comprehensiveness of the provided information.