In an experimental study like a usability
test, data are collected on different measures, such as how long
it takes to complete a task. Task completion time (called Time
on Task) is a dependent variable; among other things, it
depends upon the content of each task and upon how experienced
each test participant is with the product under study.
In a within-subjects design, the values of the dependent
variable for a task or a set of tasks (for example, tasks involving
making an online purchase) are compared with the values for another
task or another set of tasks (for example, tasks in which items
are added to an online bridal registry) within one participant's
data. In other words, within-subjects designs are designs in which
the same variable is measured repeatedly on the same participant
under different task conditions.
