Usability Metric: Duration

As mentioned in yesterday's entry, the duration it takes for a user to complete a functional task is an important metric in usability requirements. However, there are really two types of duration:

1. Engagement duration - the amount of time the user is actively attending to the task.
2. Total duration - the total amount of time it takes for the task to complete.

Consider, for example, disk defragmenting software. A user performs miminal configuration and initiates the defragmenting process. The amount of time the user is engaged in these activities might just be a few seconds. But the total amount of time it takes to achieve the user's goal - defragmenting the disk - could take hours.

You might argue that the total duration doesn't so much measure ease of use as it does performance or productivity. Either way, it is a separate concept from engagement duration.