References

Bangor, A., P. Kortum and J. Miller, 2009. Determining what individual SUS scores mean: Adding an adjective rating scale. J. Usability Stud., 4: 114-123.
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Bevan, N., J. Carter and S. Harker, 2015. ISO 9241-11 Revised: What have we Learnt About Usability Since 1998?. In: Human-Computer Interaction, Kurosu, M. (Ed.). Springer, Berlin, Germany, ISBN:978-3-319-20900-5, pp: 143-151.

Nielsen, J., 2006. Quantitative studies: How many users to test?. Nielsen Norman Group, Fremont, California.

Sauro, J., 2010. What to do with task times when users fail a task. Usability LLC, USA. http://www.measuringu.com/blog/failed-times.php.

Sauro, J., 2011. A Practical Guide to the System Usability Scale (SUS). Measuring Usability LLC, USA. http://www.measuringu.com/sus.php.

Sauro, J., 2011. What is a good task-completion rate?. Usability LLC, USA. http://www.measuringusability.com/blog/task-completion.php.