AFQT scores are the primary measure of recruit potential. Figure 2.7 indicates the percentage of NPS recruits who scored at or above the 50th percentile (Categories I–IIIA) since FY 1973. Numerical data are in Appendix D, Table D-12. The drop in Category I–IIIA recruits after FY 1976 was due primarily to the miscalibration of the ASVAB.  In FY 1976, when new versions of the ASVAB were introduced, an error in calibrating the score scales made the new versions "easier" than the old versions (i.e., applicants received test scores higher than their actual ability). In FY 1980, an independent study of the calibration was made and the test was correctly calibrated. Then, Congress added legal provisions stipulating that no more than 20 percent of accessions could be in Category IV and that such accessions had to be high school diploma graduates.  However, as previously stated, Defense Planning Guidance decreases this limit even further, allowing no more than 4 percent of recruits to come from Category IV.
After adopting the test in 1976 the test became a way of indicating whether or not an individual was 100% qualified to serve. As previously mentioned this aptitude test has a colorful history. That is because it underwent a dramatic change in 2002 and another dramatic change in 2004. The change that occurred in 2002 expanded the categories of the test and the overall difficulty. This can be seen by the addition of all of the diverse categories below:
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The Armed Services Vocational Aptitude Battery is the most widely used multiple-aptitude test battery in the world. As an aptitude test, the ASVAB measures your strengths, weaknesses, and potential for future success. The ASVAB also provides you with career information for various civilian and military occupations and is an indicator for success in future endeavors whether you choose to go to college, vocational school, or a military career.
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.