A Beginner's Guide to the System Usability Scale (SUS)
Are you curious about how user-friendly a website, app, or product is? Wondering how to measure its usability? Enter the System Usability Scale, (SUS) a simple yet powerful tool designed to gauge the user-friendliness of systems and products. In this beginner’s guide, we’ll walk you through what SUS is and how to use it effectively. 🙁 😐 🙂 😃
Understanding the System Usability Scale (SUS)
The System Usability Scale, commonly referred to as SUS, is a widely used questionnaire-based method for assessing the usability of software, websites, or any system that involves human interaction. SUS was developed by John Brooke in the 1980s and has since become a go-to tool for usability professionals, researchers, and product designers.
Why Use the System Usability Scale?
- User-Centric Evaluation — SUS focuses on gathering feedback from users, putting their experiences and opinions at the forefront of the evaluation process.
- Quick and Easy — It’s a straightforward and quick method that can be administered to users within minutes, making it an efficient way to gather usability data.
- Quantitative Results — SUS provides a numerical score, allowing for easy comparison of different systems or versions. This can help you track improvements over time.
- Standardised — Because of its widespread use, SUS has established benchmarks for usability, making it easier to interpret results in the context of industry standards.
How to Use the System Usability Scale (SUS)
Using SUS involves a simple process, typically consisting of the following steps:
- Prepare the SUS Questionnaire
The SUS questionnaire consists of ten statements that users are asked to respond to. Each statement is rated on a scale from 1 (strongly disagree) to 5 (strongly agree).
Here are the ten statements:
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.
2. Administer the SUS Questionnaire
Invite users who have interacted with your system to participate in the SUS evaluation. Explain the purpose of the questionnaire and assure them that their honest feedback is valuable.
3. User Responses
Ask participants to rate each of the ten statements based on their experiences with the system. They should choose a number from 1 to 5, where 1 means “strongly disagree” and 5 means “strongly agree.”
4. Calculate the SUS Score
To calculate the SUS score for a particular user, follow these steps:
For odd-numbered questions (1, 3, 5, 7, 9), subtract 1 from the user’s score. For even-numbered questions (2, 4, 6, 8, 10), subtract the user’s score from 5.
5. Sum up all the adjusted scores.
Multiply the sum by 2.5 to get the final SUS score.
The SUS score can range from 0 to 100, with a higher score indicating better usability.
5. Interpret the Results
Interpreting SUS results involves understanding what the score means in the context of your system. Here’s a rough guideline:
85 and above: Excellent usability
70–84: Good usability
50–69: Okay usability
Below 50: Poor usability
6. Iterate and Improve
The real value of SUS lies in its ability to help you identify areas where your system can be improved. Use the feedback from participants to make changes to your system and then re-administer the SUS to see if usability has improved.
📌 Let’s calculate SUS scores
Let’s assume we have the following user responses to the ten statements of the SUS:
Step 1: For each question with a positive orientation (questions 1, 3, 5, 7, and 9), decrease the participant’s response by one. Responses will vary between zero and four.
Example:
- Participant score: 5 (strongly agree)
- Subtract 1 from the participant’s answer: 5–1=4
Step 2: For each question with a negative orientation (questions 2, 4, 6, 8, and 10), subtract the participant’s response from five. Responses will vary between zero and four.
Example:
- Participant score: 5 (Strongly agree)
- Subtract 5 from participant’s answer: 5–5 = 0
Step 3: We sum the adjusted scores. The total scores can vary between 0 and 40.
Sum: 3+4+2+3+4+3+3+4+3+2= 31
Multiply the sum by 2.5 to get the SUS score: 31 * 2.5 = 77,5 (SUS)
Interpretation of Results
In this context, a score of 77.5 indicates good usability, which means that users generally found the system easy to use and had a positive experience. 😃
The SUS scale ranges from 0 to 100, and a score of 77.5 falls into the category of very strong usability.
This is a positive outcome, suggesting that the majority of users had a favorable experience with the system. However, for continuous improvement, it’s advisable to delve into users' qualitative feedback. Analysing their comments can provide insights into specific areas that contributed to the high score and reveal opportunities for refinement and enhancement in the user experience. This iterative process is essential for evolving and optimizing your designs over time.
Now…
…let’s imagine that the result was 45. ☹️
If the result on the SUS scale is 45, indicating poor usability, it is crucial to take the following steps to improve the system:
- Individual Response Analysis – Examine responses to each question on the SUS scale to identify problematic areas.
- Understanding Qualitative Feedback – Analyse user comments to comprehend specific difficulties encountered.
- Comparison with Usability Standards – Consider industry usability standards to contextualise the score and guide further improvements. (Note that these usability standards refer to the 10 Usability Heuristics for User Interface Design).
- Continuous Design Improvement – Based on the analysis, iterate on the design, prioritising areas that significantly impact usability.
- Reapplication of the SUS Scale – After implementing improvements, reassess usability with the SUS scale to measure the impact.
- Request for Additional Feedback – Seek additional feedback from users to assess the effectiveness of changes and understand their expectations.
- Planning for Future Evaluations – Establish plans for future evaluations, maintaining a continuous improvement cycle.
Remember, design is an iterative process, and ongoing user feedback is essential for enhancing usability and overall satisfaction. 📈🙂
Conclusion
In conclusion, the System Usability Scale is a valuable tool for beginners and experts alike in usability testing. It offers an efficient and user-centric approach to evaluating the usability of systems and provides actionable insights for improvement. So, whether you’re designing a website, app, or any user interface, consider incorporating SUS into your usability testing toolkit to create user-friendly experiences.
In this article, you’ll find a list of the most valuable websites related to the System Usability Scale.
