Final answer:
The dimension of design quality that involves consistency of performance over time or the probability of failure is called reliability. It is a critical factor in product design, ensuring that products consistently perform as expected without failure.
Step-by-step explanation:
The dimension of design quality that concerns the consistency of performance over time or the probability of failing is known as reliability. Reliability relates to how likely a product or service is to perform consistently and without failure over its expected lifetime. This concept is crucial in the design phase of products as engineers must focus on creating prototypes that not only meet initial quality standards but also retain their performance reliability over time. In specific, it pertains to the repeatability of a product's performance given the same conditions, which is a much-valued attribute in the marketplace.
When prototypes are not tested adequately, there's a greater chance that the reliability of the product might not be accurately assessed, potentially leading to failures that could have been prevented with more thorough testing. Thus, reliability is a key measure used to evaluate the quality of a design, making sure that it delivers a consistent level of performance throughout its life.