Human factors are the primary causal factor aviation accidents.[12] In 1999, the National Aeronautics and Space Administration, NASA, testified before the U.S. House of Representatives that pilot fatigue impacts aviation safety with "unknown magnitude". The report cited evidence of fatigue issues in areas including aviation operations, laboratory studies, high-fidelity simulations, and surveys. The report indicates that studies consistently show that fatigue is an ongoing problem in aviation safety.[13] In 2009, Aerospace Medical Association listed long duty work hours, insufficient sleep, and circadian disruptions as few of the largest contributing factors to pilot fatigue.[14] Fatigue can result in pilot error, slowed responses, missed opportunities, and incorrect responses to emergency situations.