Would it be okay to use 2 SUS scores to come up with a single score in the case I explain below:

I conducted a user testing for a banking mobile app, the app under investigation has lots of tasks which stakeholders wants to look up so, in order to keep the testing session around an hour I divided the tasks in 2 groups. Each performed 5 tasks. After the test, each group was presented with SUS. I have 2 SUS scores in hand, one comes from Group 1 performed task A,B,C,D,E and other from Group 2 performed task F,G,H,I. All tasks belong to the same mobile app. Is it ok to get combine the results of these two in order end up with a single score for the app itself?


Depends on the system, but quite unlikely.

SUS has an unique way to measure questions, so you can't just combine results and take averages. Also, it's recommended to measure only one task at the time, because measuring multiple tasks at once may invalidate results since participants may alter these. For example, because they already know the system or because they're tired and annoyed.

If you have these individual tasks identified, then I'd recommend you present the SUS scale for each task. Otherwise, simply explain:

"we divided the research process in 2 groups. Group 1 did A, B, C, D, E tasks with teh following results ........."

and same for group 2

  • Hi Devin, sure I do the maths in a way that SUS requires. I thought SUS is more likely to be presented at the end of test sessions since it is interest is quantifying the system as a whole, also not seems convenient represent 10 questions to the participant after each task. Am I wrong? – Izzie Jan 16 '19 at 7:23
  • What was the same for two test sessions: participant profiles, the app, number of tasks. The difference: Tasks itself. The second group encountered with some set which requires further knowlegde on the domain hence they had difficult times due to the lack of support given by the app. – Izzie Jan 16 '19 at 7:24
  • But still you support merging these 2 scores (SUS style math) is not correct? – Izzie Jan 16 '19 at 7:26

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