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A concept in product design, sometimes referred to as ease of use or user-friendliness, that is related directly to the quality of the product and indirectly to the productivity of the work force. Customer surveys show that product quality is broken down into six components (in descending order of importance): reliability, durability, ease of maintenance, usability, trusted or brand name, and price. Ease of maintenance and usability both relate to product usability. Reliability also has a component of usability to it. If a product is too difficult to use and thus appears not to work properly, the customer may think that it has malfunctioned. Consequently, the customer may return the product to the store not because it is unreliable but because it does not work the way the customer thinks it should. See Human-computer interaction
There are five criteria by which a product's usability can be measured, including time to perform a task, or the execution time; learnability; mental workload, or the mental effort required to perform a task; consistency in the design; and errors. The usability of a product usually cannot be optimized for all five criteria at the same time. Trade-offs will occur. As an example, a product that is highly usable in terms of fast execution times will often have poor usability in terms of the time needed to learn how to use the product. A product designer must be aware that it may not be possible for a product to be highly usable by all usability criteria, and so design according to the criteria that are most important to potential customers. Casual users of a product will have different demands on a product compared to expert users. See Control systems, Human-factors engineering, Human-machine systems
Many companies, especially computer or consumer electronics companies, have laboratories in which to test the usability of their products. The methods of usability testing are formal experimentation, informal experimentation, and task analyses. Although laboratory methods for improving usability can increase the cost of the product design, the benefits (market share, productivity) will outweigh the costs. See Methods engineering, Optimization