A critical assessment of the program in 2010 by the Government Accountability Office noted that aviation officials began the behavior program in 2003, in the wake of the Sept. 11 attacks, without first determining if it had a scientific basis.

Nine years later, this question remains largely unanswered, even as the agency moves to expand the program, the accountability office said in a follow-up report last year. It said that until the agency is able to better study and document the validity of the science, Congress might consider freezing tens of millions of dollars budgeted for the program’s growth.