The ASVAB also known as the Armed Services Vocational Aptitude Battery is a test that measures your aptitude which is how well you do something. A common mistake by most people is thinking that it is a measure of you IQ. Many people either forget this or don’t know this and they get worked up about the exam. Saying that, it is also important to take a ASVAB sample test to insure you know what type of questions will be asked. Another thing to keep in mind is every person in the armed forces has to take the exam and you are not being called out to take it.
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).