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.