What is a measurable usability goal?
A measurable usability goal is the definition of successful usability on your site for a specific set of users doing a specific task.
Example: You are building a Web application for owners of small businesses to pay state withholding tax online. You might set these measurable usability goals:
A business owner who has been paying withholding tax by mailing in a check and slip every month will now pay that tax online. On the first attempt, the business owner will:
- successfully complete the transaction in five minutes or less
- submit the right amount from the right bank and bank account
- make no more than one error while using the application
- recover from any error in one minute or less
- rate the experience a four or five on a one to five scale where five is the best
- indicate a desire to use the application for future tax payments
What types of measurable usability goals should you set?
Typical usability goals include:
- Time
- Accuracy
- Overall success
- Satisfaction
Time
You can set a usability goal for the overall time the user will take to carry out a task (scenario) on the site. You can also break down that time and set measurable usability goals for:
- time to get to the application or to the right Web information page
- time to use the application or to understand the information
- time to recover from an error
Accuracy
Similarly, you can set a usability goal for the accuracy with which the user carries out the task (scenario) or you can break it down into separate goals for:
- number of unproductive navigation choices
- number of unproductive searches
- number of errors in using an application
- number of misunderstandings of information
Overall success
Obviously, the usability goal must be that users will be successful. If users cannot do their tasks or cannot get answers to their questions on your Web site, your Web site is failing those specific users for those specific tasks and questions.
You may also set measurable usability goals for how users will get to that success. For example, you might set a measurable usability goal for a Web application that new users will go to the help if they need it, will find what they need in the help, and will be back doing their original task within two minutes. You might set a measurable usability goal that a user who has done the task in your Web application before will do it successfully a second time without using the help.
Satisfaction
Again, obviously, your measurable usability goal must be that users are happy. You can measure overall satisfaction. You can also break down satisfaction and set separate measurable usability goals for navigation, search, level of detail in the content, language of the content, and other specific factors.
Which types of measure should you rely on most?
When you test the Web site against your measurable usability goals, consider performance (time, accuracy, success) as more important than satisfaction ratings. If users give the site low ratings, the site needs to be fixed. If users give the site high ratings, you may not be getting a true picture. In usability testing, we often find that users give high satisfaction ratings even when they have had serious performance problems. They may be blaming themselves for the problems. They may not want to hurt your feelings. They may be being polite rather than saying what they really think.
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