System Usability Scale
What is it?
The most common measure of customer attitude toward usability is the System Usability Scale (SUS). The SUS is a series of 10 Likert-scale questions and produces a score from 0–100.

Can be linked to the NPS score.
How it Works?
SUS is a post-test questionnaire which means it administered at the end of a usability session. They reflect on how users perceive the usability of the application as a whole.
What Measures?
SUS score above 68 is considered above average and anything below 68 is below average.

What are the Pros and Cons?
This metric do not tell us why users struggle with a design, nor do they provide direct insights as to how we can improve it. They simply are a way of keeping track of how the users feel about the experience of using a product or service.

  • Have a free normed database of scores.
  • The biggest advantage to using the SUS is that it's such an old scale that there is a large amount of industry-wide data available to help benchmark your score and understand it in the context of your peers and competitors
  • SUS correlates strongly with a much simpler metric, the single-question Net Promoter Score;
  • SUS is considered a technology-agnostic questionnaire, meaning the items aren't specific to any technology or platform.

  • Complex scoring method promising to mistakes because a 0–100 score is not equivalent to a percentage score;
    • To score the SUS, follow these steps:
      1. For odd items, subtract 1 from the user response.
      2. For even-numbered items, subtract the user responses from 5. This scales all values from 0 to 4 (with 4 being the most positive response).
      3. Add up the converted responses for each user and multiply that total by 2.5. This converts the range of possible values from 0 to 100 instead of from 0 to 40.
      4. Average together the scores for all participants
  • User impressions of the experience as a whole are subject to the peak-end effect (that is, the most intense and last parts of the experience, either positive or negative, impact participants' recollections and evaluations the most);
  • it doesn't address usefulness or utility.
What SUS Covers?
t consists of 10 items that users rate from Strongly Disagree (1) to Strongly Agree (5).

  1. I think that I would like to use this system frequently.
  2. I found the system unnecessarily complex.
  3. I thought the system 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 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.
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