What is computerized adaptive testing?

Computerized adaptive tests (CATs) are a sophisticated method of test delivery based on item response theory (IRT). They operate by adapting both the difficulty and number of items.

Difficulty: Most characterizations of adaptive testing focus on how item difficulty is matched to examinee ability. High ability examinees receive more difficult items, while low ability examinees receive easier items, which has important benefits to the student and the organization. An adaptive test typically begins by delivering an item of medium difficulty; if you get it correct, you get a tougher item, and if you get it incorrect, you get an easier item. This basic algorithm continues until the test is finished, though it usually includes subalgorithms for important things like content distribution and item exposure.

Number: A less publicized facet of adaptation is the number of items. Adaptive tests can be designed to stop when certain psychometric criteria are reached, such as a specific level of score precision. Some examinees finish very quickly with few items, so that adaptive tests are typically about half as many questions as a regular test, with at least as much accuracy. Because some examinees have longer tests, these adaptive tests are referred to as "variable-length." Obviously, this makes for a massive benefit: cutting testing time in half, on average, can substantially decrease testing costs. Nevertheless, some adaptive tests use a fixed length, and only adapt item difficulty. This is merely for public relations issues, namely the inconvenience of dealing with examinees who feel they were unfairly treated by the CAT, even though it is arguably more fair and valid than conventional tests.

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