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Objective To assess whether higher mortality rates among individuals in motor vehicle crashes in areas with low population density depend on injury type and severity or are related to the performance of emergency medical services (EMS). Methods Prehospital and hospital deaths were studied in a population-based cohort of 41 243 motor vehicle crashes that occurred in Sweden between 1998 and 2004. The final multivariable analysis was restricted to 6884 individuals in motor vehicle crashes, to minimise the effects of confounding factors. Results Crude mortality rates following motor vehicle crashes were inversely related to regional population density. In regions with low population density, the unadjusted rate ratio for prehospital death was 2.2 (95% CI 1.9 to 2.5) and for hospital death 1.5 (95% CI 1.1 to 1.9), compared with a high-density population. However, after controlling for regional differences in age, gender and the type/severity of injuries among 6884 individuals in motor vehicle crashes, low population density was no longer associated with increased mortality. At 25 years of age, predicted prehospital mortality was 9% lower (95% CI 5% to 12%) in regions with low population density compared with high population density. This difference decreased with increasing age, but was still 3% lower (95% CI 0.5% to 5%) at 65 years of age. Conclusions The inverse relationship between population density and mortality among individuals in motor vehicle crashes is related to pre-crash factors that influence the type and severity of injuries and not to differences in EMS. [ABSTRACT FROM PUBLISHER]

Background Classification of injuries and estimation of injury severity on the basis of ICD-10 injury coding are powerful epidemiological tools. Little is known about the characteristics and consequences of primary coding errors and their consequences for such applications. Materials and methods From the Swedish national hospital discharge register, 15 899 incident injury cases primarily admitted to the two hospitals in Uppsala County between 2000 and 2004 were identified. Of these, 967 randomly selected patient records were reviewed. Errors in injury diagnosis were corrected, and the consequences of these changes were analysed. Results Out of 1370 injury codes, 10% were corrected, but 95% of the injury codes were correct to the third position. In 21% (95% CI 19% to 24%) of 967 hospital admissions, at least one ICD-10 code for injury was changed or added, but only 13% (127) had some change made to their injury mortality diagnosis matrix classification. Among the cases with coding errors, the mean ICD-based injury severity score changed slightly (difference 0.016; 95% CI 0.007 to 0.032). The area under the receiver operating characteristics curve was 0.892 for predicting hospital mortality and remained essentially unchanged after the correction of codes (95% CI for difference -0.022 to 0.013). Conclusion Errors in ICD-10-coded injuries in hospital discharge data were common, but the consequences for injury categorisation were moderate and the consequences for injury severity estimates were in most cases minor. The error rate for detailed levels of cause-of-injury codes was high and may be detrimental for identifying specific targets for prevention. [ABSTRACT FROM AUTHOR]