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System Usability Scale (SUS)
The System Usability Scale (SUS) is a widely used, easy-to-administer questionnaire that measures a system’s usability. It is quick to implement and provides a reliable, quantifiable score, although it’s generalized and lacks specific feedback on usability issues.
SUS consists of a 10-item questionnaire with five positively worded and five negatively worded statements.
The user is asked to rate their level of agreement with each statement on a 5-point Likert scale, ranging from Strongly Disagree (1) to Strongly Agree (5).
Scoring: The SUS score is calculated by converting individual responses into numerical values, which are then summed and normalized to produce a final score.
Scoring: The SUS score is calculated by converting individual responses into numerical values, which are then summed and normalized to produce a final score.
This score is usually scaled to fall between 0 and 100, with higher scores indicating better usability.
It takes just a few minutes for users to complete, making it ideal for usability testing.
Reliable
The SUS has been validated through numerous studies and is considered a reliable tool for assessing usability.
Broad Applicability
It can be used across various types of systems (e.g., websites, mobile apps, software) and is versatile for different user bases.
Easy to Interpret
The normalized score is straightforward to interpret, providing a clear measure of overall usability.
While the SUS provides a general usability score, it doesn't dive into specific usability issues or user needs.
Subjectivity
Since it is based on users’ perceptions, the score may not always reflect specific usability problems that require more in-depth analysis.
No Benchmarking
A score of 68 is often considered average, but it can vary widely depending on the context, making it difficult to compare SUS scores across different domains or industries.
Nominal Scale
Advantages of using SUS
Quick and SimpleIt takes just a few minutes for users to complete, making it ideal for usability testing.
Reliable
The SUS has been validated through numerous studies and is considered a reliable tool for assessing usability.
Broad Applicability
It can be used across various types of systems (e.g., websites, mobile apps, software) and is versatile for different user bases.
Easy to Interpret
The normalized score is straightforward to interpret, providing a clear measure of overall usability.
Limitations of SUS
Generalizing the ScoreWhile the SUS provides a general usability score, it doesn't dive into specific usability issues or user needs.
Subjectivity
Since it is based on users’ perceptions, the score may not always reflect specific usability problems that require more in-depth analysis.
No Benchmarking
A score of 68 is often considered average, but it can vary widely depending on the context, making it difficult to compare SUS scores across different domains or industries.
Common SUS Questions:
- I think that I would like to use this system frequently.
- I found the system unnecessarily complex.
- I thought the system was easy to use.
- I think that I would need the support of a technical person to be able to use this system.
- I found the various functions in this system were well integrated.
Types of Scaling in UX Research
Scaling refers to the process of categorizing or rating user feedback based on different criteria. In UX research, scaling is often used to measure attitudes, preferences, and perceptions through structured numeric values or categories.Nominal Scale
The nominal scale is used for categorical data, where items are placed into distinct, non-ordered categories. This type of scale assigns numbers or labels to items but doesn’t indicate any ranking or order.
Example: Gender (Male, Female, Other), Product categories (Electronics, Furniture, Clothing).
Ordinal Scale
Example: Gender (Male, Female, Other), Product categories (Electronics, Furniture, Clothing).
Ordinal Scale
The ordinal scale ranks items based on order or preference, but the distances between the rankings are not necessarily equal. It can show relative positions but doesn't provide exact measurements.
Example: Satisfaction rating (Very Unsatisfied, Unsatisfied, Neutral, Satisfied, Very Satisfied), Performance rankings (1st place, 2nd place, 3rd place).
Interval Scale
The interval scale has equal intervals between values, but it doesn’t have a true zero point. This scale can represent both order and exact differences between values, but a score of zero doesn’t indicate the absence of the property being measured.
Example: Temperature (measured in Celsius or Fahrenheit), Date and time (calendar years, but without an absolute zero).
Ratio Scale
The ratio scale is the most advanced form of scaling, with equal intervals and a true zero point, meaning that zero represents the complete absence of the attribute being measured. It is often used for quantitative data.
Example: Time (measured in seconds, minutes), Age (measured in years), Revenue (measured in dollars).
Example: Satisfaction rating (Very Unsatisfied, Unsatisfied, Neutral, Satisfied, Very Satisfied), Performance rankings (1st place, 2nd place, 3rd place).
Interval Scale
The interval scale has equal intervals between values, but it doesn’t have a true zero point. This scale can represent both order and exact differences between values, but a score of zero doesn’t indicate the absence of the property being measured.
Example: Temperature (measured in Celsius or Fahrenheit), Date and time (calendar years, but without an absolute zero).
Ratio Scale
The ratio scale is the most advanced form of scaling, with equal intervals and a true zero point, meaning that zero represents the complete absence of the attribute being measured. It is often used for quantitative data.
Example: Time (measured in seconds, minutes), Age (measured in years), Revenue (measured in dollars).