According to ISO 9241-11, usability is defined as “the extent to which a system, product or service can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use”. There are several usability assesssment methods that should be used early in the development process, however, these methods can be applied in all phases of the design cycle (e.g., early concept testing, diagnostic testing, and benchmark testing) (Dumas, Salzman, 2006).
Types of usability evaluations and variations of each:
Usability testing is used to identify the strengths and weaknesses of a system. Typically, usability testing is conducted by having participants complete tasks with the system or product. Quantitative data such as, error and success rates can be collected. Qualitative data such as, participant satisfaction can also be collected.
Think-alouds are often utilized in usability tests. The main aim of think-alouds is to have the user articulate areas where they had trouble using a system, interface, product, etc. Think-alouds can be retrospective (after doing a task) or concurrent (while doing a task).
Interviews can be conducted to uncover a large amount of information from a small sample size. Interviews can give more information on the user's thought process, motivations, and needs.
Unstructured: questions are within context of task but there is no use of standardized questions
Structured: use of previously formed questions, making it easier to replicate
Semistructured: provides a set of topics for discussion without scripted questions, most commonly used
Surveys are used to measure subjective ratings of usability (i.e., perceived usability) typically with Likert-type scales. Possbile questions may focus on comfortability, ease of use, and frustration.
Short questionnaires can be used as an efficient measure to collect reactions to a product that has just been used (e.g., System Usability Scale)
Long questionnaires often include subscales within the questionnaire (e.g., The Computer User Satisfaction Inventory and the Questionnaire for User Interaction Satisfaction)
Inspections take the form of expert reviews (i.e., usability specialist reviews product or system from point of view of the user) or walkthroughs (i.e., discussion of task steps with usability specialist, developers, and project manager). Inspections are useful for finding problems in a system, but not necessarily solutions to those problems.
References:
1. Dumas J. S., Salzman M. C. (2006) Usability Assessment Methods. Reviews of Human Factors and Ergonomics. 2(1), 109-140. doi:10.1177/1557234X0600200105
2. ISO (2018). Ergonomics of human-system interaction: Usability: Definitions and concepts. https://www.iso.org/obp/ui/#iso:std:iso:9241:-11:ed- 2:v1:en>
3. Olmsted-Hawala, E.L., Murphy, E.D., Hawala, S., & Ashenfelter, K.T. (2010). Think-aloud protocols: a comparison of three think-aloud protocols for use in testing data-dissemination web sites for usability. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems.