Ever wondered how to truly measure how user-friendly your product is? The System Usability Scale (SUS) might just be your secret weapon. Let’s explore what makes it so powerful and how you can master it.
Understanding the System Usability Scale (SUS)
The System Usability Scale (SUS) is a simple, ten-item scale giving a global view of subjective assessments of usability. Developed by John Brooke in 1986, it has become one of the most widely used tools for measuring the usability of a system.
What is SUS?
SUS is a questionnaire consisting of 10 statements with five response options ranging from Strongly Agree to Strongly Disagree. It’s a quick and reliable tool to assess usability.
- Originally developed for digital systems
- Applicable across various industries
- Provides a single score representing overall usability
Why SUS Matters
Usability is a core aspect of user experience. A product that’s hard to use will fail, regardless of how powerful it is. SUS helps quantify that experience.
“Usability is not only about effectiveness and efficiency, but also about satisfaction.” — ISO 9241-11
History and Evolution of SUS
Understanding the origins of SUS gives us better insight into its robustness and adaptability.
Origin of SUS
SUS was created by John Brooke while working at Digital Equipment Corporation. It was designed to be a “quick and dirty” usability scale that could be used for a wide range of systems.
Adaptations Over Time
Since its inception, SUS has been adapted to suit various contexts, including mobile apps, websites, and even hardware interfaces.
- Translated into multiple languages
- Applied in healthcare, education, and enterprise software
- Used in both formative and summative testing
Structure and Scoring of the SUS
The structure of the SUS allows for a simple, yet comprehensive scoring system that is easy to interpret.
The 10 Questions
The scale includes alternating positive and negative statements to reduce response bias. For example:
- I think that I would like to use this system frequently.
- I found the system unnecessarily complex.
Scoring Methodology
Each item is scored on a scale of 0 to 4. The scores are then summed and multiplied by 2.5 to convert the total to a 0–100 scale.
“A SUS score above 68 is considered above average.” — Jeff Sauro, MeasuringU
Benefits of Using the System Usability Scale
SUS is popular for a reason. It offers several unique advantages that make it ideal for usability testing.
Quick and Easy
SUS can be administered in under 5 minutes, making it perfect for iterative testing.
Reliable and Valid
Despite its simplicity, SUS has been proven to be both reliable and valid across various domains.
- High internal consistency
- Strong correlation with other usability metrics
- Validated in over 1300 studies
Limitations and Criticisms
While SUS is powerful, it’s not without its flaws. Understanding these helps in using it more effectively.
Lack of Diagnostic Power
SUS provides a usability score but doesn’t tell you what went wrong. It’s best used in conjunction with qualitative methods.
Interpretation Challenges
Some users find interpreting the SUS score challenging. What does a score of 72 really mean? Context is key.
“SUS scores are not percentages. A score of 70 does not mean 70% usable.” — Nielsen Norman Group
How to Administer SUS Effectively
To get the most out of SUS, it’s important to administer it correctly and consistently.
When to Use SUS
SUS can be used:
- After usability testing sessions
- During A/B testing
- As a benchmark over time
Best Practices
Ensure anonymity, avoid leading questions, and combine with other usability methods like think-aloud protocols.
Interpreting SUS Scores
Once you have your SUS score, the real work begins—making sense of it.
Score Ranges
- Below 50: Poor usability
- 50–68: Average usability
- Above 68: Good usability
Benchmarking
Compare your SUS scores to industry standards or previous versions of your product to track improvement.
Real-World Applications of SUS
SUS is used in a wide range of industries to improve product usability.
Healthcare
Used to evaluate electronic health record systems and medical devices.
Education
Applied to learning management systems and educational apps to improve student experience.
Enterprise Software
Helps in assessing complex software used in corporate environments.
Combining SUS with Other UX Methods
SUS works best when used alongside other UX research tools.
Qualitative Methods
Pair SUS with user interviews or usability testing to gain deeper insights.
Quantitative Metrics
Combine SUS with task success rates, error rates, and time on task for a holistic view.
Advanced Topics in SUS
For those who want to go beyond the basics, there are advanced ways to use and interpret SUS.
Statistical Analysis
Use tools like SPSS or R to analyze SUS scores across user groups or over time.
Item-Level Analysis
Look at individual question responses to identify specific usability issues.
Resources and Tools
Several online tools and resources can help you implement SUS more effectively.
Frequently Asked Questions
What is a good SUS score?
A score above 68 is generally considered good. However, context matters and comparisons to past scores or industry standards are essential.
Can SUS be used for mobile apps?
Yes, SUS is versatile and can be applied to almost any system, including mobile applications.
Is SUS a replacement for usability testing?
No, SUS complements usability testing by providing a quantitative measure. It should not replace observational methods.
How many users are needed for SUS?
While SUS can be used with as few as 5 users, larger samples provide more reliable data.
Can I modify the SUS questions?
It’s not recommended to change the core questions as it may affect the validity of the scale.
In conclusion, the System Usability Scale is a powerful, flexible, and easy-to-administer tool that provides valuable insights into the usability of a product. Whether you’re a UX designer, product manager, or researcher, SUS can help you make data-driven decisions to improve user experience.
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