Comparison between two quasi-induced exposure methods for studying risk factors for road crashes

This study was designed to compare estimates from two quasi-induced exposure methods of the effects of driver- and vehicle-related conditions on the risk of causing a road crash for drivers of vehicles with four or more wheels. From the Spanish register of road crashes with victims, the authors selected, for 1993-2002, all 755,329 drivers of >or=4-wheeled vehicles involved in single-vehicle crashes or in two-vehicle collisions in which only one of the drivers was considered responsible. Multinomial and logistic regression models were used to obtain the odds ratio for each driver- and vehicle-related variable. Construction of these models was based on the assumptions of classical quasi-induced exposure methods and on the method (a paired-by-collision analysis of responsible and nonresponsible drivers) proposed by Perneger and Smith (Am J Epidemiol 1991;134:1138-45). The main driver-dependent conditions for any type of crash were psychophysical circumstances (alcohol use and sleepiness). The effect of most driver- and vehicle-related characteristics was higher for single-vehicle crashes than for two-vehicle collisions. Furthermore, both classical and paired-by-collision analyses yielded similar estimates and can be considered equally useful alternatives for assessing the effect of driver and vehicle characteristics on the risk of causing a collision between two vehicles.