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Valuing Usability Programs

by Kristoffer Bohmann, July 14, 2000

Practical tools to cost-benefit analyze usability programs.

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Assume that a website has 10.000 users per month each performing 10 tasks in the period. What will be the economic effect of a usability study that promises 40 seconds faster user task performance? One way to make the calculation is shown below.

The first step is to calculate the saved user hours per year as Number of users * Tasks per user * Estimated time savings per task. Next, the economic effect of the time savings is found using this formula: Saved user hours * User value per hour. Finally, economic impact of usability evaluation: Probability of implementing the intended design improvement is assumed to be 30 percent better when conducting usability evaluation before designing. So, economic impact of usability evaluation equals: Total Savings Per Year * Improved results due to usability evaluation.

Table 1: Valuing Usability Program Example

Users per year (10.000 per month) 120.000 per year
Tasks per user (10 per month) 120 per year
Estimated time savings per task (40 seconds) 0,0111 hours
Saved user hours per year 160.000
Estimated user value per hour $20
Total Savings Per Year $3.200.000
P(successful design|usability evaluation) 90%
P(success design|no usability evaluation) 60%
Probability of better results due to usability evaluation 30%
Economic Impact of Usability Evaluation $960.000
Source: Calculation technique inspired by comment made by Jakob Nielsen.

Information Needed

To make the calculation information is needed about:


The calculation is based on several assumptions. First, the most important assumption is that the user task is the primary level of analysis in usability studies, while page views are secondary. Effective usability efforts strive to improve overall user tasks often spanning several pages, while single Web pages only are improved to the extent they affect task performance.

Next, the user task is an aggregated level often containing several design elements and Web pages - this is especially so in interaction design. The basic unit of analysis is the design component such as a headline, URL, or graphical item. Tasks are improved through more appropriate use of design components.

Finally, the distinction between level and unit of analysis is important to carry out purposeful usability efforts that focus on critical dimensions in the user interface. So, this approach has a fundamental assumption about user behavior: Users use websites to solve tasks, not to see single pages or design components.

About the Author
Kristoffer Bohmann (biography) M.Sc. thinks and writes about high-quality user experiences. His philosophy: Users first. You can contact him at

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