Estimating seat belt effectiveness using matched-pair cohort methods
ABSTRACT Using US data for 1986-1998 fatal crashes, we employed matched-pair analysis methods to estimate that the relative risk of death among belted compared with unbelted occupants was 0.39 (95% confidence interval (CI) 0.37-0.41). This differs from relative risk estimates of about 0.55 in studies that used crash data collected prior to 1986. Using 1975-1998 data, we examined and rejected three theories that might explain the difference between our estimate and older estimates: (1) differences in the analysis methods; (2) changes related to car model year; (3) changes in crash characteristics over time. A fourth theory, that the introduction of seat belt laws would induce some survivors to claim belt use when they were not restrained, could explain part of the difference in our estimate and older estimates; but even in states without seat belt laws, from 1986 through 1998, the relative risk estimate was 0.45 (95% CI 0.39-0.52). All of the difference between our estimate and older estimates could be explained by some misclassification of seat belt use. Relative risk estimates would move away from 1, toward their true value, if misclassification of both the belted and unbelted decreased over time, or if the degree of misclassification remained constant, as the prevalence of belt use increased. We conclude that estimates of seat belt effects based upon data prior to 1986 may be biased toward 1 by misclassification.
- SourceAvailable from: Xuedong Yan
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- "In some cases, pairs can share characteristics that are unmeasurable (e.g. Cummings et al., 2003b; Martin and Lenguerrand, 2008; Viano et al., 2008), and a more classic example of this would be twin studies. Similarly to the latter, this study in fact constructs a dataset with observations of inherently matched pairs, because each pair of drivers originates from the same accident and experienced the same weather, the same crash location, the same road geometry, etc. "
ABSTRACT: This study seeks to inspect the nonparametric characteristics connecting the age of the driver to the relative risk of being an at-fault vehicle, in order to discover a more precise and smooth pattern of age impact, which has commonly been neglected in past studies. Records of drivers in two-vehicle rear-end collisions are selected from the general estimates system (GES) 2011 dataset. These extracted observations in fact constitute inherently matched driver pairs under certain matching variables including weather conditions, pavement conditions and road geometry design characteristics that are shared by pairs of drivers in rear-end accidents. The introduced data structure is able to guarantee that the variance of the response variable will not depend on the matching variables and hence provides a high power of statistical modeling. The estimation results exhibit a smooth cubic spline function for examining the nonlinear relationship between the age of the driver and the log odds of being at fault in a rear-end accident. The results are presented with respect to the main effect of age, the interaction effect between age and sex, and the effects of age under different scenarios of pre-crash actions by the leading vehicle. Compared to the conventional specification in which age is categorized into several predefined groups, the proposed method is more flexible and able to produce quantitatively explicit results. First, it confirms the U-shaped pattern of the age effect, and further shows that the risks of young and old drivers change rapidly with age. Second, the interaction effects between age and sex show that female and male drivers behave differently in rear-end accidents. Third, it is found that the pattern of age impact varies according to the type of pre-crash actions exhibited by the leading vehicle.Accident; analysis and prevention 06/2014; 67:129–136. DOI:10.1016/j.aap.2014.02.021 · 1.65 Impact Factor
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- "This method normalizes crashes by dividing the number of fatalities in a specific group of occupants to the number of fatalities in a control group. It has been used to estimate the effectiveness of restraint systems and seating positions by various researchers (Dalmotas and Krzyzewski 1987, Evans 1987, 1988, Cummings et al. 2003). "
ABSTRACT: Effectiveness of the rear seat in protecting occupants of different age groups in frontal crashes for 2000-2009 model years (MY) of vehicles was estimated and compared to 1990-1999 model years of vehicles. The objective was to determine the effectiveness of the rear seat compared to the front seat for various age groups in newer model year vehicles. The double paired comparison method was used to estimate relative effectiveness. For belted adults of the 25-49 age group, the fatality reduction effectiveness of the rear seat compared to the right front seat was 25 % (CI 11% to 36%), in the 1990-1999 model year vehicles. The relative effectiveness was -31% (CI -63% to -5%) for the same population, in the 2000-2009 model year vehicles. For restrained children 0-8 years old, the relative effectiveness was 55% (CI 48% to 61%) when the vehicles were of the 1990-1999 period. The level of effectiveness for this age group was reduced to 25% (CI -4% to 46%) in the 2000-2009 MYs of vehicles. Results for other age groups of belted occupants have followed a similar trend. All belted adult occupants of 25+ years old were significantly less protected in rear seats as compared to right front seats in the 2000-2009 model years of vehicles. For unbelted occupants however, rear seats were still a safer position than front seats, even in the 2000-2009 model years of vehicles.Annals of advances in automotive medicine 01/2010; 54:149-58.
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- "Many studies have assessed the effect of individual variables, such as age, sex, safety belt use and seating position in the vehicle on the risk of death or severe injury to the driver or passengers of vehicles involved in road crashes (Bédard et al., 2002; Braver et al., 1998; Cummings et al., 2003b; Evans, 2001a,b; Huelke and Compton, 1995; Li et al., 2003; O'Donnell and Connor, 1996; Smith and Cummings, 2004; Yau, 2004; Zhang et al., 2000). To control for the confounding effect of crash severity (for example, the protective effect of the driver's safety belt may be overestimated if unbelted drivers tend to be involved in more severe crashes), some researchers have applied matched-byvehicle analyses, either with the double pair comparison method proposed by Evans (1986) or with the more efficient regression matched-pair analysis methods (Cummings et al., 2003a). "
ABSTRACT: We studied the effect of age, gender, use of restraint systems and seat position on the risk of death for rear-seated passengers of cars involved in road crashes. The data source was the Spanish register of traffic crashes with victims compiled by the Government's General Traffic Directorate. Data for crashes recorded from 1993 to 2002, inclusive, were studied. We used a matched cohort design to analyze all 5260 rear-seated passengers in vehicles occupied by two or three rear-seated passengers for accidents in which at least one of these passengers was killed. Conditional Poisson regression with death as the dependent variable was used. An increased risk of death was observed for females and children aged <3 years. For passengers aged 25 years and older, the risk increased with age. The use of restraint systems and central and right-side seats was associated with a lower risk. These results should be considered in research focused on passenger fragility and strategies to prevent injury and death.Accident Analysis & Prevention 06/2006; 38(3):563-6. DOI:10.1016/j.aap.2005.11.014 · 1.87 Impact Factor