When you are considered a career in the military you need to take the ASVAB test. But each branch of the military has different ASVAB requirements that you need to meet. They are different levels of education that you must reach to take the test. But you also need to score a certain amount of points on that ASVAB test to gain access into the branch you desire.
The IRT model underlying ASVAB scoring is the three-parameter logistic (3PL) model. The 3PL model represents the probability that an examinee at a given level of ability will respond correctly to an individual item with given characteristics. Specifically, the item characteristics represented in the 3PL model are difficulty, discrimination (i.e., how well the item discriminates among examinees of differing levels of ability), and guessing (i.e., the likelihood that a very low ability examinee would respond correctly simply by guessing).
The Armed Forces Qualifying Test, commonly known as the AFQT, is used by the United States military to assess prospective service members. The questions on this test are taken from the Armed Forces Vocational Aptitude Battery. The following ASVAB subject areas are included in the test: arithmetical reasoning (AR), mathematics knowledge (MK), verbal expression (VE), paragraph comprehension (PC), and word knowledge (WK). These are the most general academic content areas on the ASVAB. The formula for computing scores on the AFQT test is AR + MK + (2 x VE), with VE = PC + MK. Scores are then placed in the following categories: Category I (93 to 99), Category II (65 to 92), Category IIIA (50 to 64), Category IIIB (31 to 49), Category IVA (21 to 30), Category IVB (16 to 20), Category IVC (10 to 15), and Category V (0 to 9). These AFQT test score categories are percentiles, which indicate how well the test-taker performed relative to others. A person scoring a 50, for example, performed as well as or better than half of the other test-takers. The percentile score is based on the raw score (number of questions answered correctly) and the difficulty of the test version. The minimum passing score for the AFQT varies between branches of the military.
One ASVAB sub-measure, the Armed Forces Qualification Test (AFQT)--which is just a separate analysis of the same tests that focuses only on four of the subtests--is also population-referenced, but its score from 1-99 is a percentile score. This means that if you score a 73, you scored as well as or higher than 73% of test-takers in the national sample.