Active shooter drills became one of the most common school safety measures implemented nationwide in recent years, despite widespread fears that the procedures heighten anxiety, and evidence that school shooters, like the one in Parkland, Florida, use knowledge of the drills to their advantage. Teachers unions in February called for schools to not conduct active shooter drills with students. Now, new research adds data to those concerns.

A report released Thursday, obtained in advance by NBC News, found active shooter drills in schools correlated with a 42 percent increase in anxiety and stress and a 39 percent increase in depression among those in the school community, including students, teachers and parents, based on their social media posts.