System Usability Scale

The questionnaire is a “quick and dirty” option to measure usability.

This quantitative quick-and-dirty method can be used to measure usability. It collects data that can be quantitatively evaluated and interpreted: users answer questions about the application. The result is a percentage usability value of the application or service that has been evaluated. 

The simple questionnaire consists of ten questions based on Likert scales with five options. The questionnaire contains five positive and five negative statements. Brooke proposes the following ten statements that can and should be adapted to individual circumstances. 

  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.

The test participants answer these questions using Likert scales ranging from complete rejection to full approval. 

Each answer gets values from 0 to 4. The value depends on the formulation: Positively formulated specifications receives the value 4 for full agreement and 0 for disagreement and vice versa. 

Based on the results you get the so-called SUS-score. It ranges between 0 (worst imaginable application) and 100 (best imaginable application). The numbers of each questions are added together (the sum ranges between 0 and 40) and then multiplied by 2.5. 

After several test persons have been tested an average SUS score can be calculated. This average value is not but can be interpreted as a percentage.

  • 100% corresponds to a perfect system without usability problems.
  • Values above 80% indicate good to excellent usability.
  • Values between 60% and 80% are interpreted as borderline to good.
  • Values below 60% are indications of significant usability problems.

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