Madison Waldron has an app on her phone that, on the surface, looks and acts a lot like a fitness tracker. But then there are the survey questions it pushes out to her:

"Questions in regards to what I do for a living, education and things like that," she says as she thumbs through her phone, showing her scheduled doctor visits. "And I get questions as far as my sexual history and my practices."

For the next two years, Waldron and hundreds of other transgender women will be peppered with questions through this app. It's a core part of the LITE ("Leading Innovation for Transgender Women's Health and Empowerment") study at the University of Miami, which is designed to better understand HIV risks among transgender women.

The estimates for HIV rates among trans women are extremely high—the Centers for Disease Control and Prevention estimates a quarter of trans women live with HIV. But, says researcher Dr. Allan Rodriguez, "this population has been understudied, it's not really understood, and that's why this study is being done."

He and his colleagues hope that by collecting data on trans women who are HIV negative, they'll be able to better identify not just what puts them at risk, but what protects their health.

"We can't necessarily ask for policy change if we don't have the data behind it," says Dr. Andrew Wawrzyniak, one of the researchers on the project.

You can learn more about the study, including how to participate, at litestudy.org.