A mathematical model of the finding of usability problems

@article{Nielsen1993AMM,
  title={A mathematical model of the finding of usability problems},
  author={Jakob Nielsen and Thomas K. Landauer},
  journal={Proceedings of the INTERACT '93 and CHI '93 Conference on Human Factors in Computing Systems},
  year={1993}
}
  • J. Nielsen, T. Landauer
  • Published 1 May 1993
  • Computer Science
  • Proceedings of the INTERACT '93 and CHI '93 Conference on Human Factors in Computing Systems
For 11 studies, we find that the detection of usability problems as a function of number of users tested or heuristic evaluators employed is well modeled as a Poisson process. [] Key Result For a “medium” example, we estimate that 16 evaluations would be worth their cost, with maximum benefit/cost ratio at four.

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References

SHOWING 1-10 OF 33 REFERENCES
Refining the Test Phase of Usability Evaluation: How Many Subjects Is Enough?
TLDR
Three experiments are reported in this paper that relate the proportion of usability problems identified in an evaluation to the number of subjects participating in that study, finding that 80% of the usability problems are detected with four or five subjects.
Finding usability problems through heuristic evaluation
Usability specialists were better than non-specialists at performing heuristic evaluation, and “double experts” with specific expertise in the kind of interface being evaluated performed even better.
User interface evaluation in the real world: a comparison of four techniques
TLDR
A user interface for a software product was evaluated prior to its release by four groups, each applying a different technique: heuristic evaluation, software guidelines, cognitive walkthroughs, and usability testing.
Streamlining the Design Process: Running Fewer Subjects
TLDR
An experiment conducted to determine the minimum number of subjects required for a usability test finds that with between 4 and 5 subjects, 80% of the usability problems are detected and that additional subjects are less and less likely to reveal new information.
Estimating the number of subjects needed for a thinking aloud test
  • J. Nielsen
  • Computer Science
    Int. J. Hum. Comput. Stud.
  • 1994
Abstract Two studies of using the thinking aloud method for user interface testing showed that experimenters who were not usability specialists could use the method. However, they found only 28-30%
Iterative user-interface design
TLDR
A method for developing user interfaces by refining them iteratively over several versions, which not only eliminates problems of this nature, but also allows designers to take advantage of any insights into user needs that emerge from the tests.
The usability engineering life cycle
TLDR
It is shown that the most basic elements in the usability engineering model are empirical user testing and prototyping, combined with iterative design.
When Should One Stop Testing Software
Abstract We derive an optimal rule for stopping the testing of a module of software prior to release, based on the trade-off between the cost of continued testing and the expected losses due to any
Usability inspection methods
  • J. Nielsen
  • Computer Science
    CHI 95 Conference Companion
  • 1995
Usability inspection is the generic name for a set of costeffective ways of evaluating user interfaces to find usability problems. They are fairly informal methods and easy to use.
Cost/benefit analysis for incorporating human factors in the software lifecycle
TLDR
Methodologies for improvement of the interface design, an overview of the human factors element, and cost/benefit aspects are explored.
...
...