Estimating seat belt effectiveness using matched-pair cohort methods

Harborview Injury Prevention and Research Center, 325 Ninth Avenue, Box 359960, Seattle, WA 98104-2499, USA.
Accident Analysis & Prevention (Impact Factor: 1.87). 02/2003; 35(1):143-9. DOI: 10.1016/S0001-4575(01)00087-2
Source: PubMed


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.

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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. "
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    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
    • "It has been estimated that using seat belts can reduce the risk of fatalities in a RTC by 40-50% among front seat occupants and by 25-75% among rear seat car occupants.[34] This effectiveness of seat belts in reducing the severity of injury in vehicle occupants involved in collisions has been proven all over the world.[256789] "
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    ABSTRACT: Seat belts are designed to reduce injuries due to road crash among vehicle occupants. This study aims to determine the availability of seat belt in vehicles and compliance with seat belt use among vehicle occupants. This was a 24-h direct observational study of seat belt usage among vehicle occupants in Makurdi, Benue State, Nigeria. By direct surveillance and using a datasheet, we observed 500 vehicles and their occupants for seat belt availability and compliance with its use. Chi-square test was used for test of significance between variables. Twenty-five (5.0%) of the observed 500 vehicles had no seat belt at all. Overall, compliance was 277/486 (57.0%). Use of seat belt was highest in the afternoon with 124/194 (64.4%), followed by 111/188 (59.0%) in the morning and 42/95 (44.2%) at night. Compliance was highest among car occupants [209/308 (67.9%)] and private vehicles, and lowest among commercial vehicle occupants. Compliance among female drivers was 77.1% compared with 51.4% among male drivers. Among drivers, the mean age of seat belt users was 38.4 (7.7) years, which was significantly younger than the 41.3 (8.7) years mean age of non-users. Similar figures were obtained among other vehicle occupants. Compared with previous studies, seat belt usage has improved among Nigerian road users, but there is still room for improvement, especially early in the mornings and at nights. Since these were times when law enforcement agencies were not likely to be on the roads, we advocate for improved coverage by enforcement agents to enforce better compliance.
    03/2013; 3(3):427-432. DOI:10.4103/2141-9248.117950
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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). "
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    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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