In the paper and pencil (P&P) ASVAB, every examinee is given the same items, regardless of his/her ability level. In order to accurately measure ability across all examinees, the P&P-ASVAB includes items that range from very easy to very hard. However, administering easy items to high-ability applicants is inefficient. Usually, high-ability applicants answer these items correctly so these easy items provide little information about high-ability applicant's ability levels. The same inefficiencies are true for administering hard items to low-ability applicants. The most accurate measurement occurs when the difficulty of the items is matched to the examinee's level of ability.

In the CAT-ASVAB, the test is tailored to each examinee. Items are selected for administration from a pool of items that range in difficulty from very easy to very hard. After each item is administered, information is collected and evaluated, and the item best suited for the examinee's estimated ability level is selected to be administered next. This adaptive item selection process results in higher levels of test-score precision and shorter test lengths than the P&P-ASVAB.

The figure below illustrates that shorter test lengths can be achieved on the CAT-ASVAB by tailoring the test to the ability level of each examinee.

Typically, if an examinee answers an item incorrectly on the CAT-ASVAB, an easier item is selected to be administered next. If an examinee answers an item correctly, then a harder item is selected to be administered next. The item selection process for the CAT-ASVAB is illustrated in the figure below.

The branching utilized in the CAT-ASVAB ensures that examinees will be administered items best suited to their abilities. Item selection, however, is just one step in the CAT-ASVAB process. The figure below shows the complete sequence of steps that are followed during the CAT-ASVAB.

The first item administered in the CAT-ASVAB is of average difficulty. Subsequent items are selected to match the examinee's estimated ability. After each item is administered, the test time is evaluated. If the time limit is not exceeded and the test is not completed, then an interim ability estimate is computed for the examinee and another item is selected for administration. The process is repeated until either the test is completed or time runs out. Then a final ability estimate is computed, and a final score on the ASVAB is reported.

A penalty procedure is applied to all examinees who do not complete the test before time runs out. This is done by scoring the items that were not completed as though they were answered at random. In almost all cases it is not necessary to apply the penalty, as the time constraints are liberal enough that nearly all examinees are able to complete each subtest.

For more information about CAT-ASVAB test times and test lengths, click here.

For more information about how ability estimates, penalties, and final scores are computed, click here.

More technical details about the CAT-ASVAB are presented in ASVAB Technical Bulletin #1, ASVAB Technical Bulletin #2, ASVAB Technical Bulletin #3 and in Sands, Waters, & McBride (1997).