Introduction
In the realm of user experience (UX) and human-computer interaction (HCI), evaluating the usability of a system is crucial. One of the most widely used tools for this purpose is the System Usability Scale (SUS). Developed by John Brooke in 1986, SUS provides a quick and reliable way to measure the usability of a variety of products and services, from software and websites to hardware and mobile devices.
What is the System Usability Scale (SUS)?
SUS is a simple, ten-item Likert scale questionnaire that users complete after interacting with a system. Each item is a statement that the respondent can agree or disagree with, using a five-point scale ranging from “Strongly agree” to “Strongly disagree.” The questions are designed to cover a broad range of aspects related to the user’s interaction with the system, providing a holistic view of its usability.
Structure of the SUS Questionnaire
The SUS questionnaire consists of ten statements, with responses scored from 1 (strongly disagree) to 5 (strongly agree). The statements alternate between positive and negative to prevent response bias. Here are the ten items typically included in a SUS questionnaire:
1. I think that I would like to use this system frequently.
2. I found the system unnecessarily complex.
3. I thought the system was easy to use.
4. I think that I would need the support of a technical person to be able to use this system.
5. I found the various functions in this system were well integrated.
6. I thought there was too much inconsistency in this system.
7. I would imagine that most people would learn to use this system very quickly.
8. I found the system very cumbersome to use.
9. I felt very confident using the system.
10. I needed to learn a lot of things before I could get going with this system.
Scoring the SUS
Scoring SUS involves a specific method:
1. For odd-numbered items, subtract 1 from the user’s response.
2. For even-numbered items, subtract the user’s response from 5.
3. Sum the scores for each item, then multiply the total by 2.5 to convert the original scores to a 0-100 scale.
The final score, ranging from 0 to 100, represents the overall usability of the system, with higher scores indicating better usability. However, it is important to note that SUS scores are not percentages but are relative values that provide a general sense of the system’s usability.
Interpreting SUS Scores
A SUS score provides a quantitative measure of usability, but what does a particular score mean? According to research and practical applications, the following guidelines can help interpret SUS scores:
– 85-100: Excellent usability
– 70-84: Good usability
– 50-69: Acceptable usability
– Below 50: Poor usability
These ranges can help UX professionals and designers understand how well their system performs and identify areas for improvement.
Advantages of Using SUS
SUS offers several benefits, making it a popular choice for usability testing:
1. Simplicity: The questionnaire is straightforward and easy for users to complete.
2. Versatility: It can be used to evaluate a wide range of systems and products.
3. Reliability: SUS has been shown to provide consistent and reliable results across different contexts.
4. Benchmarking: The scale allows for comparison between different systems or versions of the same system.
Conclusion
The System Usability Scale (SUS) is a powerful tool for assessing the usability of systems and products. Its simplicity, versatility, and reliability make it a valuable asset for UX professionals aiming to create user-friendly experiences. By understanding and utilizing SUS, organizations can gain valuable insights into their systems’ performance, ensuring that their products meet users’ needs and expectations effectively.
References
– Brooke, J. (1996). SUS: A quick and dirty usability scale. In P. W. Jordan, B. Thomas, B. A. Weerdmeester, & I. L. McClelland (Eds.), Usability Evaluation in Industry (pp. 189-194). London: Taylor and Francis.
– Bangor, A., Kortum, P., & Miller, J. (2008). An Empirical Evaluation of the System Usability Scale. International Journal of Human-Computer Interaction, 24(6), 574-594.
By leveraging the insights provided by SUS, organizations can drive continuous improvement in their system designs, ultimately enhancing user satisfaction and success.
