Direct commission: civilians who have special skills that are critical to sustaining military operations and supporting troops may receive direct commissions. These officers occupy leadership positions in law, medicine, dentistry, pharmacy, intelligence, supply-logistics-transportation, engineering, public affairs, chaplain, oceanography and others.
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).