Reality Check: Are 15,000 transgender people serving in the US military?
The claim: It has been widely shared on social media and elsewhere that there are 15,000 transgender people serving in the US military.
Reality Check verdict: There is no official data to rely on, but the most recent research available estimates there are no more than 10,790 transgender individuals on active duty or in reserve forces.
When President Trump made a surprise announcement in July about his plans to ban transgender people from serving in the US military "in any capacity", claims that this affected 15,000 current service personnel quickly gained traction.
It was quoted by celebrity activist Caitlyn Jenner, among many others, who tweeted that there were "15,000 patriotic transgender Americans in the US military fighting for all of us".
Actress and singer Barbra Streisand also tweeted the figure, arguing the ban "puts a target on 15,000 active military members".
But is the number accurate?
Until very recently, it was not possible to join the American armed forces if you were openly transgender.
The full policy was due to be implemented by 1 July, 2017.
Prior to President Trump's unexpected announcement, Mr Carter's plan was moving forward, although in June 2017 the current Defence Secretary, James Mattis, had announced a six-month delay to the implementation deadline.
The proposed changes had already prompted some service personnel to publicly identify themselves as transgender.
However, neither the US government nor the military collect official statistics about the number of transgender personnel.
Instead, we have to look at other sources.
The figure of 15,000 appears to come from a 2014 study from UCLA Law School's Williams Institute on Sexual Orientation and Gender Identity Law and Public Policy.
It estimated that 15,500 transgender individuals were on active duty or serving in the guard or reserve forces.
The report was based on surveys of transgender individuals, one of which collected data as far back as 2008, and suggested "transgender individuals are more likely than the general population to serve in the US military".
This research was commissioned by the US Department of Defense to help estimate the cost implications of allowing transgender individuals to serve openly, such as, for example, additional medical costs.
The researchers looked at all the available sources (including the UCLA study) to create an estimate.
But they faced a number of problems.
Significantly, there were no official or scientific studies that gave an estimate of the number of transgender individuals in the country as a whole.
The surveys that they did look at were out-of-date, or covered only certain states.
They looked at social security data to look for changes of name and gender.
Using the limited available information, they created an estimate suggesting that there could be between 1,320 and 6,630 transgender individuals in the military, out of about 1.3 million personnel.
On top of that, they calculated that there could be between 830 and 4,160 in the reserves.
So, that would make a maximum estimate of 10,790.
They also estimated that each year, between 29 and 129 service members in the active component would seek transition-related care that could disrupt their ability to deploy.
When it comes to transgender individuals in the US as a whole, or the American military, we don't have any official or rigorous epidemiological research to rely on.
From the studies that are available, it seems that 15,000 might be too high an estimate. But it would still represent only 0.75% of active and reserve personnel.