Effectiveness of usability evaluation

Do you ever wonder how effective expert reviews and usability tests are? Apparently, they can be pretty good.

Rolf Molich and others have conducted a series of comparative usability evaluation (CUE) studies, in which a number of teams evaluate the same version of a web site or application. The teams chose their own preferred methods—such as an expert review or a usability test. Their reports were then evaluated and compared by a small group of experts.

What the first six CUE studies found

About 30% of reported problems were found by multiple teams. The remaining 70% were found by a single team only. Fortunately, of that 70%, only 12% were serious problems. In one CUE study, the average number of reported problems was 9, so a team would be overlooking 1 or 2 serious problems. The process isn’t perfect, but teams found 80% or more of the serious problems.

Teams that used usability testing found more usability problems than expert reviewers. However, expert reviewers are more productive-they found more issues per hour-as this graph from the fourth CUE study illustrates:

CUE study 4 results

Teams that found the most usability problems (over 15 when the average was 9) needed much more time than the other teams, as illustrated in the above graph. Apparently, finding the last few problems takes up the most time.

The CUE studies do not consider the politics of usability and software development. Are your developers sceptical of usability benefits? Usability studies provide credibility-boosting video as visual evidence. Are your developers using an Agile method? Expert reviews provide quick feedback for each iteration.

To learn more about comparative usability evaluation, read about the findings of all six CUE studies.