22. Product Performance

A key element of the definition of the requirements of a product is the expected performance of the product under its usage or operating conditions. The performance requirements need to be measurable. Therefore performance requirements should usually be accompanied by an associated test requirement. The performance measures below are an indication of the type of performance requirements often associated with a product.

Accuracy

Accuracy is a common measure of a product's performance. It gives a view of the tolerances of the product and therefore an indication of the uses to which it may be put.

Capacity

Capacity indicates the storage or operational performance of the product. Capacity measures are not an indication of the efficiency of the product though they are often construed as such. A capacity measure simply indicates potential, not an actuality.

Efficiency

One of the key performance criteria is the efficiency of a product or system. In general efficiency is a ratio of outputs to inputs. The output and input units may differ and so we see efficiency measured as a rate of throughput where the time element is an input. Similarly efficiency may be measured as a consumable cost per unit of output.

Effectiveness

Another way of viewing performance is in terms of a product's effectiveness. Effectiveness is a relationship between the actual inputs and outputs and the corresponding objectives for the product. Thus typical effectiveness measures relate the efficiency of the product to the target capital costs of the product. Similarly measures such as error rate, rejection rate and responsiveness define the effectiveness of the system relative to its efficiency parameters.

Reliability

Product reliability is an important consideration in any product definition. There are a variety of measures of product reliability and different products have different requirements in each of the areas of reliability. There are a variety of reasons why a product must fulfil basic reliability requirements. These can range from a need to ensure the safety of the users to the need to achieve a particular level of security or integrity of information