What is the SUS test?
In today’s digital age, ensuring that software systems and products are user-friendly and intuitive is crucial for their success. One of the most widely used methods for evaluating the usability of such systems is the System Usability Scale (SUS) test.
SUS test
The SUS test is a questionnaire-based method for evaluating the effectiveness of a system, product, or service. It comprises a standardized set of questions to measure the user’s perception of usability. Developed by John Brooke in 1986, the SUS test has since become a popular tool for usability evaluation in various fields, including software development, web design, and product manufacturing.
How does the SUS test work?
The SUS test typically comprises ten questions, each rated on a 5-point Likert scale ranging from “Strongly disagree” to “Strongly agree.” The questions encompass aspects like ease of use, learnability, efficiency, and overall satisfaction with the system. Users are asked to complete the questionnaire based on their experience using the system.
SUS score and calculation
To calculate SUS scores for individual questions in the survey, assess each respondent’s answer using five available response options. Each question is evaluated individually, one at a time.
Proceed with the following steps to compute SUS scores:
Expressing responses into numeric values
Every option in the survey is given a number to represent the respondent’s feedback. This helps turn subjective opinions into numerical data for analysis.
- Strongly agree: 5 points
- Agree: 4 points
- Neutral: 3 points
- Disagree: 2 points
- Strongly disagree: 1 point
Determine values for x and y
The ten statements in the SUS survey are categorized into even-numbered and odd-numbered questions to facilitate calculation.
x is calculated by subtracting 5 from the total points of all odd-numbered questions.
y is calculated by subtracting 25 from the total points of all even-numbered questions.
Determine the SUS score
The ultimate SUS score is calculated with the help of the formula:
The equation above integrates values of x and y to derive the SUS score, reflecting the perceived usability of the system.
Let’s suppose the sum of points for all odd-numbered questions is 20. Therefore,
Suppose the sum of points for all even-numbered questions is 25. Therefore,
SUS interpretation
Once the questionnaire responses are collected, the scores are aggregated and normalized to produce a usability score ranging from 0 to 100. A higher SUS score indicates better usability, with scores above 70 considered above average and scores below 68 indicating potential usability issues. The SUS test provides a quantitative measure of usability, allowing researchers and designers to objectively assess the overall user experience.
Grade | SUS | Adjective |
A+ | 84.1-100 | Best Imaginable |
A | 80.8-84.0 | Marvellous |
A- | 78.9-80.7 | Excellent |
B+ | 77.2-78.8 | Best |
B | 74.1 – 77.1 | Very Good |
B- | 72.6 – 74.0 | Good |
C+ | 71.1 – 72.5 | Above Average |
C | 65.0 – 71.0 | Average |
C- | 62.7 – 64.9 | Below Average |
D | 51.7 – 62.6 | OK |
F | 25.1 – 51.6 | Poor |
F | 0-25 | Worst Imaginable |
In the preceding section, we computed the SUS Score, which is valued at 37.5. Let's assign a grade to this score using the SUS interpretation table. Since it falls within the range of 25.1-51.6, its grade should be F, indicating poor performance.
Importance of the SUS test
The SUS test offers several benefits for evaluating system usability:
Standardized evaluation: The SUS test provides a standardized framework for evaluating usability across different systems and products.
Quick and easy: The questionnaire format makes it quick and easy to administer, allowing for rapid usability assessment.
User-centric feedback: By soliciting feedback directly from users, the SUS test provides valuable insights into user perceptions and preferences.
Objective measurement: The SUS score provides an objective measure of usability, enabling researchers and designers to compare different systems and track improvements over time.
Conclusion
In summary, the SUS test is a valuable tool for evaluating the usability of products, services, and software systems. By providing a standardized framework for usability assessment, the SUS test helps identify areas for improvement and ultimately enhances the user experience. Whether we’re a software developer, UX designer, or product manager, incorporating the SUS test into our usability evaluation toolkit can lead to more user-friendly and successful products.
