ABSTRACT
In spite of its apparent simplicity, the event of a test taker responding to a test item is hard to disentangle, especially if the interest is both in the observed response and the time used to produce it. For one thing, the test taker's ability to solve an item is not the only factor that plays a role; the speed at which she/he operates should also be accounted for, which immediately raises the question of how the two are related. For some tests, there is more at stake for their test takers than for others, so motivation may have an impact on both as well. Similar questions arise with respect to the difficulty of the item and the amount of labor demanded by it. Besides, the nature of all these relationships is even more difficult to disentangle if the conditions change during testing; for example, due to increased fatigue toward the end of the test.
