User testing metrics - time on task

1. How do you measure time on task usability testing?
2. Is time on task recorded with every test?
3. Why is time on task not always the best measure of usability?
4. How long should user testing take?

How do you measure time on task usability testing?

During a typical usability study, simply collect the times it took to accomplish a task. The best way to do this is to measure time per screen or activity in addition to the duration of the task, so that you'll be able to isolate which step of a process is taking the most time or adding unnecessary seconds.

Is time on task recorded with every test?

Task times are collected in about half of formative usability tests and 75% of summative tests. Task times can be great for diagnosing usability problems. A long task time is often caused by problems with the interaction with the interface. Time on task can be collected even when users think aloud.

Why is time on task not always the best measure of usability?

It is very rare for usability studies to employ tasks that are so simple that users can perform them in a few seconds. Usually, it is better to have the users perform more goal-directed tasks that will take several minutes.

How long should user testing take?

To run a usability test effectively will take between 30–60 minutes per participant. Of course, depending upon the complexity of what you're building, this length of time will vary, but in my experience, an hour is about the maximum time I'd recommend.