System Usability Scale

What is the System Usability Scale?

The System Usability Scale (SUS) is a widely used tool for evaluating the usability of digital products. Developed in 1986 by John Brooke, it offers a simple, quick and inexpensive way of evaluating the usability of a system. The SUSThe questionnaire comprises ten questions covering various aspects such as user-friendliness, learning effort and integration of functions.

Structure and mode of operation

Each item in the questionnaire is assigned five possible answers on a Likert scale ranging from 1 (strongly disagree) to 5 (strongly agree). The respondents' answers are then converted into points and combined to give an overall score of between 0 and 100.

A Advantage of the SUS is its versatility: it can be used for a variety of digital products and services such as mobile applications, web applications and software. Its strength lies in its ability to quickly provide an overall usability assessment, allowing developers to gain valuable insights to optimize their products.

Advantages and disadvantages

To the Strengths of the SUS include simple handling and quick evaluation. The results can be easily interpreted and provide a good initial assessment of user-friendliness. However, a key disadvantage is that the SUS does not provide detailed insights into specific weaknesses of a product. It can therefore only be used as a rough evaluation tool that should be used in combination with more detailed usability tests and analyses.

Definition and meaning of usability

At UsabilityUsability is a key quality feature for evaluating the user-friendliness of user interfaces. It comprises various dimensions such as efficiency, effectiveness and satisfaction, which together determine how well users can achieve their goals with a system. A high level of usability is essential to ensure that digital products can be operated intuitively and are therefore competitive.

Dimensions of usability

The core aspects of usability include:

• Efficiency: How quickly can users complete their tasks with the system?
• Effectiveness: How precisely and completely can users achieve their goals?
• Satisfaction: How pleasant do users find working with the system?

These factors play a decisive role in assessing the usability of a product and directly influence its acceptance on the market.

Importance in product development

User research and usability tests should be carried out at every stage of product development. Continuous usability testing can ensure that the end product is not only technically mature, but also user-friendly. This is particularly important as poor usability often leads to frustration and ultimately user churn.

The implementation of usability tests such as the System Usability Scale provides a structured way to collect valuable feedback from users and make targeted improvements. In today's highly competitive digital world, outstanding usability can make the difference between a product's success and failure.

The structure of the System Usability Scale questionnaire

The System Usability Scale (SUS)The questionnaire consists of ten pre-defined statements covering different aspects of a system's usability. These statements were selected from an initial pool of 50 potential questions and are based on feedback from a test group of 20 people. Each of the ten statements is rated on a five-point scale. Likert scale ranging from "strongly disagree" to "strongly agree".

Typical questions in the SUS questionnaire

The structure of the questionnaire includes both positive and negative statements in order to ensure a balanced view of usability:

• I think I would use this system frequently (positive).
• I found the system unnecessarily complex (negative).
• I thought the system would be easy to use (positive).
• I think I would need help from technical people to be able to use this system (negative).
• I found that the various functions in this system were well integrated (positive).
• I think there are too many inconsistencies in this system (negative).
• I would imagine that most people learn to use this system very quickly (positively).
• I found the system very cumbersome to use (negative).
• I felt very confident in using the system (positive).
• I had to learn a lot of things before I got to grips with the system (negative).

Mixing positive and negative statements helps to minimize bias and gain a deeper insight into the usability of a system. Ultimately, the SUS questions aim to provide a comprehensive picture of the user experience and identify potential areas for improvement.

Calculation and interpretation of SBS points

The Calculation of SBS points begins by converting the answers to ten questions into numerical values. Positive items are given points from 1 to 5, while negative items are scored in reverse. Each question in the questionnaire is assigned a point value, which is then processed as follows:

• For the positive questions: The answer value (between 1 and 5) minus 1.
• For the negative questions: 5 minus the answer value (between 1 and 5).

The sum of these values is then multiplied by 2.5 to obtain a final value between 0 and 100.

Interpretation of the SUS points

The final SUS value provides a quantitative assessment of the usability of a system:

• Over 80.3: Almost perfect usability.
• Over 68: Average to good usability.
• 51-70: Marginal usability.
• Under 50: Unacceptable usability.

Some areas are clearly defined, for example, scores below 50 are considered unacceptable, while scores above 80.3 indicate almost perfect user-friendliness.

Such a differentiated evaluation helps developers and designers to recognize whether their product performs well in terms of usability or whether there is an urgent need for improvement. High scores improve the chances of the product's market launch and acceptance, while low scores require targeted optimization measures.

Areas of application and use of the SUS

The System Usability Scale (SUS) is used in a variety of ways to evaluate the user-friendliness of digital products. It is used in various areas such as mobile applications, web applications and various digital services. Thanks to its ease of use and quick evaluation, the SUS is particularly popular in the early phases of product development and in ongoing usability tests.

Wide range of applications

The most important areas of application of the SUS include

• Rough evaluation: Before extensive usability tests are carried out, the SUS provides an initial assessment of a product's suitability for use.
• Comparison of tasks: The SUS can be used to compare the usability of different tasks within a test.
• Across versions: It makes it possible to compare the usability of different versions of a product or software.
• Multiple interviews: Test participants can be interviewed several times in order to observe the development of usability over time.

The use of the SUS is particularly valuable for identifying trends in user satisfaction and making targeted improvements. By regularly using this standardized questionnaire, developments in usability can be systematically tracked and documented.

Overall, the SUS is therefore an indispensable tool in the usability toolkit of developers and designers to ensure that their digital products meet the high expectations of users and remain competitive.

Advantages and disadvantages of the System Usability Scale

The System Usability Scale (SUS) offers a number of advantages that make it a popular tool for usability tests. One of the greatest strengths of the SUS is its simplicity. As it consists of only ten questions, the questionnaire can be completed quickly, which minimizes the time required for test subjects. This also makes it easier to carry out several tests at short intervals. In addition, it is inexpensive and does not require extensive preparation, which makes it particularly attractive for smaller projects with a limited budget.

Advantages of the SUS

The most important advantages at a glance:

• Fast processing: Short processing time makes it possible to test many participants.
• Cost Efficiency: Low costs compared to more extensive usability tests.
• Versatility: Can be applied to various digital products, from software to websites and mobile applications.
• Simple interpretation: Results are easy to understand and provide quick insights into usability.

Despite its strong points, the SBS also has some disadvantages. One of the main criticisms is that it does not provide detailed information about specific weaknesses or problems of a system. It merely provides an overall usability rating without offering precise instructions on how to solve problems. This can make it difficult to take precise measures to improve usability.

Disadvantages of the SUS

The most important disadvantages at a glance:

• No detailed analysis: Does not identify any specific problem areas.
• No differentiation: Individual test results are not evaluated in a differentiated manner, which makes comparison difficult.
• Relatively imprecise comparisons: The comparison between two systems or versions is not always clear and does not provide precise instructions for action.

Despite these weaknesses, the SUS remains a valuable tool, especially when used in combination with other, more detailed usability tests. Its strengths and weaknesses should be carefully weighed up in order to achieve the maximum benefit for the project in question.