The figures surrounding the question of how many trans people serve in the military are primarily based on two different studies, one from the Williams Institue and another from the RAND Corporation.
The Williams Institute study from 2014 estimated “that approximately 15,500 transgender individuals are serving on active duty or in the Guard or Reserve forces.” The study suggests that “8,800 transgender individuals are currently on active duty.”
The estimate is primarily based on “the National Transgender Discrimination Survey (NTDS), which was conducted by the National Gay and Lesbian Task Force and the National Center for Transgender Equality.” One of the questions from the 70-item survey was, “Have you ever been a member of the armed forces?” The study received 6,546 “valid responses.”
A study in 2016 from the RAND Corporation, sponsored by the secretary of defense,
estimates that “the number of transgender individuals currently serving in the active component of the U.S. military at between 1,320 and 6,630 out of a total of about 1.3 million service members.” This number accounts for 0.1-0.5 percent of those serving in active military according to the RAND Corporation.
As the RAND Corporation’s study admits, “It is difficult to estimate the number of transgender personnel in the military due to current policies and a lack of empirical data.” Instead, they base their numbers on multiple surveys and estimates. “As a result, much existing research relies on self-reported, nonrepresentative survey samples,” the study notes.
The Williams Institute study estimated that there are 8,800 trans people serving in active military roles whereas the RAND Corporation study estimates between 1,320 – 6,630. The estimates for those serving in the reserves are also quite different, with the Williams Institute suggesting that 6,700 serve and the RAND Corporation estimating only 1,510.