On Jan. 5, Texas lieutenant governor Dan Patrick unveiled a bill that would require Texas residents to use the bathroom assigned to their gender at birth. The bill, officially known as Senate bill 6 (pdf), is nearly identical to another ”bathroom bill” passed last year in North Carolina.

How many people would be affected by this new law? It’s remarkably difficult to know. Most surveys don’t ask about gender identity, and—even if they do—many transgender people are reluctant to disclose their gender identity to strangers. The best estimates available come from the Williams Institute, a think tank at the University of California, Los Angeles, which has compiled estimates for all 50 states.

According to the Williams Institute’s numbers (pdf), approximately 0.66% of Texans (around 125,000 people) identify as transgender. The estimates are based on data from the Centers for Disease Control’s Behavioral Risk Factor Surveillance System, which surveys Americans on health-related issues. In 2014, the survey included the question “Do you consider yourself to be transgender?”

However, only 19 states asked the question and Texas wasn’t one of them. Researchers used demographics for the states that did ask the question to create a statistical model, which they then used to backfill estimates for the states that didn’t. The very large range of the 95% confidence interval (the lines in the graphic above) makes it clear that these are rough estimates at best.

It’s unclear if the Texas bill will pass. It has strong support from the administration, but state business groups have come out against it, citing the economic backlash that hit North Carolina after the bill there was enacted last year. And, as Texas Monthly writer R.G Ratcliffe points out, in Texas “there have been no known cases of a transgender person acting inappropriately in a bathroom.”