Proponents of higher CAFE standards also argue that the quality of the engineering design is the prime determinant of vehicular safety, not the vehicle's mass. In 2006, IIHS found that some of the smallest cars have good crash safety, and others do not. A 2003 Transportation Research Board study show greater safety disparities among vehicles of differing price, country of origin, and quality than among vehicles of different size and weight. A 2006 study discounts the importance of vehicle mass to traffic safety, pointing instead to the quality of engineering design as the primary factor.