The System Usability Scale (SUS) is a widely used tool for measuring the usability of products, systems, and services. It provides a reliable and efficient way to gather feedback from users, helping designers and developers to identify areas for improvement. To ensure valid results, it's crucial to follow best practices when administering the SUS. Here are 10 tips to help you get the most out of your SUS surveys and achieve accurate, reliable results.
Understanding the System Usability Scale
The SUS is a 10-item questionnaire that assesses the usability of a product or system. It was developed by John Brooke in the 1980s and has since become a standard tool in the field of human-computer interaction. The SUS consists of five positive and five negative statements, which are rated on a five-point Likert scale. The scores are then combined to produce a overall usability score, ranging from 0 to 100. A higher score indicates better usability.
Administering the SUS Survey
To achieve valid results, it’s essential to administer the SUS survey correctly. This includes selecting the right participants, providing clear instructions, and ensuring that respondents understand the context of the survey. Here are some tips to help you get started:
- Recruit representative participants: Choose participants who are representative of your target audience. This will help ensure that the results are relevant and applicable to your product or system.
- Provide clear instructions: Make sure participants understand the purpose of the survey and how to complete it. Provide clear instructions and examples to avoid confusion.
- Ensure participants have used the product or system: The SUS is designed to assess the usability of a product or system. Therefore, it's essential that participants have used the product or system before completing the survey.
The following table illustrates the SUS questionnaire structure:
| Item | Statement | Scale |
|---|---|---|
| 1 | I think that I would like to use this system frequently. | 1-5 (Strongly Disagree - Strongly Agree) |
| 2 | I found the system unnecessarily complex. | 1-5 (Strongly Disagree - Strongly Agree) |
| 3 | I thought the system was easy to use. | 1-5 (Strongly Disagree - Strongly Agree) |
| 4 | I think that I would need the support of a technical person to be able to use this system. | 1-5 (Strongly Disagree - Strongly Agree) |
| 5 | I found the various functions in this system were well integrated. | 1-5 (Strongly Disagree - Strongly Agree) |
| 6 | I thought there was too much inconsistency in this system. | 1-5 (Strongly Disagree - Strongly Agree) |
| 7 | I would imagine that most people would learn to use this system very quickly. | 1-5 (Strongly Disagree - Strongly Agree) |
| 8 | I found the system very cumbersome to use. | 1-5 (Strongly Disagree - Strongly Agree) |
| 9 | I felt very confident using the system. | 1-5 (Strongly Disagree - Strongly Agree) |
| 10 | I needed to learn a lot of things before I could get going with this system. | 1-5 (Strongly Disagree - Strongly Agree) |
Interpreting SUS Results
Once you’ve collected the SUS survey data, it’s time to interpret the results. The SUS score can range from 0 to 100, with higher scores indicating better usability. Here are some general guidelines for interpreting SUS scores:
- Score 0-25: The product or system has significant usability issues and may be difficult to use.
- Score 26-50: The product or system has some usability issues, but they are not severe.
- Score 51-75: The product or system has some minor usability issues, but overall it is easy to use.
- Score 76-100: The product or system has excellent usability and is easy to use.
To illustrate the interpretation of SUS results, let's consider an example:
A company conducted a SUS survey to evaluate the usability of their new website. The results showed an average SUS score of 62, indicating that the website has some minor usability issues, but overall it is easy to use. The participant feedback highlighted some issues with navigation and search functionality, which the company can address to improve the overall usability of the website.
What is the minimum number of participants required for a SUS survey?
+While there is no strict minimum, it's recommended to have at least 5-10 participants to achieve reliable results. However, the more participants you have, the more accurate and reliable your results will be.
Can I use the SUS survey for comparative studies?
+Yes, the SUS survey can be used for comparative studies. However, it's essential to ensure that the participants are familiar with both products or systems being compared and that the survey is administered consistently.
How do I calculate the SUS score?
+To calculate the SUS score, you need to follow these steps: (1) For each question, subtract 1 from the user's response. (2) Multiply the result by 2.5. (3) Add up the scores for all 10 questions. (4) The final score will be a number between 0 and 100.
In conclusion, the System Usability Scale is a powerful tool for evaluating the usability of products, systems, and services. By following the tips outlined in this article, you can ensure that your SUS surveys are administered correctly and that the results are valid and reliable. Remember to consider the usability score in conjunction with participant feedback to gain a comprehensive understanding of usability issues and areas for improvement.
