Bias in estimates of seat belt effectiveness

An objective measure of seat belt use is needed to enable us to assess their effectiveness A lack of consensus on the effectiveness of seat belts, when used, is remarkable given that belts have been standard equipment in passenger cars for more than 30 years in the highly industrialized countries. In the 1970s, examination of 19 studies of seat belt effectiveness, when used, found estimates varying from 7.5% to 85.6%. The correlation of the estimates with reported use suggested that the higher estimates were in error because of claimed use by non-users in crashes.1 Comparisons of police reported belt use by the fatally injured and survivors in front seats of the same vehicle before 1985 in the United States indicated belt effectiveness of about 40%–45%.2 Studies using this method were thought to be more valid because within-vehicle crash forces were more similar than comparisons of occupants of vehicles among a variety of types of crashes. When belt use laws were enacted in a number of states in the United States in the mid to late 1980s, belt use increased substantially and car model year specific death rates declined commensurate with a belt effectiveness of …