Monday, July 18, 2011

System Usability Scale (SUS)

I felt like we went over the SUS very quickly, so I wanted to elaborate on it a little.

Originally developed by John Brook in 1986, the System Usability Scale (SUS) is a self reported survey metric used to evaluate application usability. The survey is comprised of 10 questions that rate user satisfaction or dissatisfaction on a 5-point scale. The odd questions are positively worded and the even are negatively worded, this is done to add variation to the survey. The questions are as follows:
  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.
To score the SUS you must first change each score from the alternating 1-5 scale to a standard 0-4 scale where 0 is dissatisfied and 5 is very satisfied. To do this, you take the odd scores (positive worded scores) and subtract 1 from each score. For example, if you had a score of 5 it would now be 4 (5-1). Then you take all of the even scores and make it reverse by subtracting the score from 5. For example if you had a score of 3 it would now be a 2 (5-3). All of the scores can now be summed together and multiplied by 2.5. It is multiplied by 2.5 to make the score out of 100. If each odd score was a five and each even score was a 1, the final score would be a perfect SUS score of 100. SUS scores average at about 66% (69% Median). With 77% in the 75th percentile, anything over 80% can be considered a “good” score (Tullis & Albert, 2008).

Below are some quick reference answers.

How is the SUS used?
          The SUS is most frequently used to compare application designs

How many questions are in the SUS questionare?

Is the SUS reliable?
Multiples studies (Lewis & Sauro 2009; Bangor et al 2008) have founds the SUS to have a Cronbach’s Alpha of .90 (note anything above .7 is considered “good”)

What does the SUS try to measure?
          Effectiveness, Efficiency, Satisfaction

Please, if you have any other FAQs please ask them and I will answer (look up the answer)

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