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A new Pentagon policy that effectively bans transgender people from joining the US military and serving in their preferred gender has come into effect.

There's no precise figure for the total number with estimates ranging from 2,150 to 15,000.

So, what should we make of these figures?

When President Trump made the announcement in July 2017, that transgender people would be banned from serving in the US military "in any capacity" a figure of 15,000 serving in the military quickly gained traction on social media, with high-profile celebrities such as Caitlyn Jenner and Barbara Streisand quoting this number.

Skip Twitter post by @Caitlyn_Jenner There are 15,000 patriotic transgender Americans in the US military fighting for all of us. What happened to your promise to fight for them? https://t.co/WzjypVC8Sr — Caitlyn Jenner (@Caitlyn_Jenner) July 26, 2017 Report

The figure 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".

A more recent study was carried out by the Rand Corporation in 2016.

This research was commissioned by the US Department of Defense to help estimate the cost implications of allowing transgender individuals to serve openly, and its findings have been quoted in recent US government reports.

The report concludes that in 2016 there were a maximum of 10,790 transgender people serving in the US military and the reserves.

But the report also gives a wide possible range, with 2,150 as the minimum figure.

To reach their conclusions, the researchers looked at all the available sources (including the UCLA study).

But they say they faced a number of problems in compiling the data.

Significantly, there were no official or scientific studies that gave an estimate of the number of transgender individuals in the country as a whole.

They looked at social security data to look for changes of name and gender.

Image caption Sgt Ken Ochoa has served as a man for more than a year

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 and a minimum of 2,150,

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