The DofD does make some info public. What they report is the recruits are NOT from "America's most prosperous families" nor from the affluent socioeconomic classes. They have historically been composed of a higher percentage of black americans than they make up of the pop as a whole (which is downtrending) and of youth who may or may not have graduated high school.
edit: after reading the link at the first post, the main problem with the data referenced is relying on zip codes, which are way too large geographic/pop sources, if they really want to mine the data they should utilize block groups.
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According to DOD data, the demographic composition of the military is somewhat different than that of the similarly aged and educated segment of the civilian workforce.3 When compared to comparable civilian workers, the military had proportionately fewer Whites (67 percent in the military compared to 71 percent in the civilian workforce), partly because the military has proportionately more African Americans (17 percent in the military versus 11 percent in the civilian workforce). The representation of American Indian/Alaskan Natives in the military equals that of the civilian workforce (about 1 percent in each). Although Hispanic representation in the military has markedly increased over the last decade to 9 percent, 11 percent of the comparable civilian workforce is of Hispanic ethnicity.
Similarly, while Asian Americans/Pacific Islanders are 3 percent of the military, they comprise 5 percent of the civilian workforce. The representation of women in the military, at 16 percent, is partly impacted by military policy and federal statutes denying women access to military specialties involving ground combat. The distribution of racial/ethnic subgroups among female servicemembers differed from that of female civilian workers. For example, African Americans` representation among female servicemembers at 28 percent was higher than their 13 percent representation among civilian female workers, but Whites` representation among female servicemembers at 54 percent was below their 71 percent representation among civilian female workers. Two percent of servicemembers are not U.S. citizens. The top three foreign countries of origin identified by servicemembers who are not U.S. citizens or nationals are the Philippines, Mexico, and Jamaica. Also, DOD has not fully implemented the government-wide requirements on the collection and reporting of racial and ethnic data that were to have been implemented by January 1, 2003. The services continue to convert their data on current servicemembers` race and ethnicity and DOD`s internal monthly reports of servicemember race and ethnicity continue to use the previous racial and ethnicity categories.4 This results in racial and ethnic tabulations that cannot be clearly compared to tabulations of the U.S. population as reported by other federal agencies such as the Bureau of the Census, making it difficult for Congress to compare the military and civilian racial and ethnic compositions. The continued use of the former categories and methods may result in the undercounting of Hispanic servicemembers who belong to a minority racial subgroup.
Over the past decade the Active Component5 (AC) has met its overall recruiting goals more frequently than has the Reserve Component (RC). We found that a combination of personal, demographic, family, and societal factors influence whether or not individuals join the military. According to DOD researchers, at least half of today`s youth between the ages of 16 and 21 are not qualified to serve in the military because they fail to meet the military`s entry standards for education, aptitude, health, moral character, or other requirements. Between fiscal years 2000 and 2004, the AC annually accessed between approximately 176,400 to 183,000 nonprior-service enlisted personnel and about 17,500 to 21,500 officers. However, since fiscal year 2002, the proportion of recruits who are African Americans has declined in the AC. DOD has not routinely surveyed and reported on the socioeconomic status of its servicemembers since 1999 and has not previously routinely reported on the types of communities from which recruits are drawn. A recent DOD analysis of over 1 million recruits found that recruits came from communities representing all socioeconomic levels and, at $44,500, the median income of recruits` communities roughly equaled the $44,300 median income of the communities of civilian youths.
link