A probabilistic bias analysis on the magnitude of unmeasured confounding: The impact of driving mileage on road traffic crashes.

INTRODUCTION: Unmeasured confounding can lead to biased interpretations of empirical findings. This paper aimed to assess the magnitude of suspected unmeasured confounding due to driving mileage and simulate the statistical power required to detect a discrepancy in the effect of polypharmacy on road traffic crashes (RTCs) among older adults. METHODS: Based on Monte Carlo Simulation (MCS) approach, we estimated 1) the magnitude of confounding of driving mileage on the association of polypharmacy and RTCs and 2) the statistical power of to detect a discrepancy from no adjusted effect. A total of 1000 studies, each of 500000 observations, were simulated. RESULTS: Under the assumption of a modest adjusted exposure-outcome odds ratio of 1.35, the magnitude of confounding bias by driving mileage was estimated to be 16% higher with a statistical power of 50%. Only an adjusted odds ratio of at least 1.60 would be associated with a statistical power of about 80% CONCLUSION: This applied probabilistic bias analysis showed that not adjusting for driving mileage as a confounder can lead to an overestimation of the effect of polypharmacy on RTCs in older adults. Even considering a large sample, small to moderate adjusted exposure effects were difficult to be detected.

What triggers road traffic fatalities among older adult drivers? An investigation based on the Swedish register for in-depth studies of fatal crashes.

INTRODUCTION: Road traffic fatalities among drivers result not only from erroneous driving manoeuvres. They can also be triggered by poor mental or physical health like suicidal acts and acute disease attacks, the latter being more frequent with age. There are few studies comprising all the different triggers of fatal crashes among older drivers and on how these triggers evolve over time. This Swedish national study aims to investigate this, considering drivers 50+ years. METHOD: For the period 2010-2019, data on non-commercial car drivers aged 50 and older were extracted from the Swedish Transport Administration's in-depth studies of fatal crashes, compiled in a register encompassing all road traffic fatalities. The crash triggers reported were classified as suicide, acute disease, own manoeuvre (single or other type of crash), external, and undetermined. Total and annual frequencies were presented by crash trigger, overall and stratified by sex and age groups. RESULTS: In total, 762 fatalities were identified and with 709 of them, it was possible to classify the crash trigger: 12% resulting from suicide; 29% from acute disease; 49% from the driver's own manoeuvre; and 10% from an external crash trigger. Suicides increased from 9% in average 2010-2014 to 15% in 2015-2019 while acute disease decreased (from 32% to 27%). The overall male-to-female ratio was 4.5, and as high as 8.7 for acute disease. The relative importance of each trigger varied with age with, for instance, acute disease being more frequent in the two younger age groups; 31% for 50-64 and 52% for 65-79 years old drivers, while own manoeuvre was more prominent for drivers aged 80 and older (23%). CONCLUSION: The distribution of the four different triggers of road traffic fatalities varies only slightly over time and, a majority are triggered by the driver's own manoeuvre. However, a substantial proportion, about four out of ten,are triggered by a health condition, of which some are suicide but the major part an acute disease, mainly cardiovascular. In some instances, such crashes can be harmful to other road users. Having in mind the need for safety and mobility of older drivers and the protection of all road users, there is a need for the promotion of road safety policies that encompass a wider range of measures to help reducing the likelihood of fatal and severe crashes to happen e.g., targeting incapacitated drivers.

Fall- and collision-related injuries among pedestrians in road traffic environment - A Swedish national register-based study.

OBJECTIVE: To investigate the burden of pedestrian injuries, including pedestrian fall injuries (PFI), compared to other transport-related injuries in Sweden and document their characteristics in terms of demographics, causes, type of injuries, and severity level with a focus on long-term consequences. METHODS: Data were retrieved from the national Swedish Traffic Accident Data Acquisition register. A total of 361,531 fatalities and injuries were reported by emergency hospitals during 2010-2019, of which 127,804 were pedestrians (35%). We assessed the magnitude of PFIs and conducted comparative analyses to assess differences compared to other types of road users regarding sex, age, severity level, injury circumstances, hospital care, causes of accidents, and type of injuries. RESULTS: Pedestrians were the second largest group of traffic-related deaths in Sweden after car occupants and accounted for just over a quarter of all fatal accidents in the road traffic environment. Of the total number of pedestrian fatalities, three out of four have been in collision accidents and the others in fall-related accidents. In terms of injuries, pedestrians were the largest group among all road users, regardless of the type of accident. PFIs accounted for a third of all injuries in the road traffic environment and nearly half of all injuries resulting in permanent medical impairment (i.e., 2.2 times more long-term consequences among PFIs compared to injured car occupants). Females (particularly middle-aged and older) and older adults were overrepresented, and most PFIs occurred on urban and municipal roads. The causes were often related to maintenance (e.g., slippery surfaces such as ice, snow, leaves or gravel together with uneven pavements and roads are the cause three out of four of PFIs). Among collision injuries, the representation was almost equal for sex and age. CONCLUSIONS: Injuries and fatalities among pedestrians are a considerable issue in the road traffic environment in Sweden. Contrary to other traffic groups, the incidence has not decreased over time, meaning that this issue must be met with specific measures and address the specific risk factors they are associated with. PRACTICAL APPLICATION: Including fall accidents in the definition of traffic accidents increases the chances of getting better information about the accidents and taking preventive measures.

Medical impairment and road traffic crashes among older drivers in Sweden - A national, population-based, case-control study.

BACKGROUND: Several medical conditions are known to impair sensory, cognitive and motor functions and are associated with road traffic crashes (RTC). For the drivers of today, we lack updated knowledge on how driving-impairing conditions are associated with RTCs, across all driving-impairing conditions in a given population. We aim to determine this among older drivers in Sweden. METHODS: A national, population register-based, matched case-control study comparing acknowledged driving-impairing health conditions among all older drivers (65 years or older) involved in an injurious RTC in the period 2011-2016 (n = 13,701) with those of controls: older drivers not involved in any RTC (n = 26,525) matched to the cases by age, sex and residential area. The medical conditions, extracted from the National Patient Register from 1997 up until date of RTC, were identified based on ICD-10 diagnosis codes and categorized into the 13 groups of medical conditions listed in the Swedish driver's license regulations. Conditional logistic regression was used to estimate crude and adjusted odds ratios (ORs) with 95% confidence intervals. RESULTS: Unadjusted ORs for RTC were increased for all conditions. After taking the other 12 medical conditions into account, the ORs remained significant in 11 out of the 13. A strong association was found for the group "ADHD and autism spectrum disorders" (OR 2.79, CI 1.47-5.30), although with very low prevalence among cases (0.2%). Moderate associations were found for three conditions with a case prevalence between 1.3% and 8.5%: epilepsy and seizure disorders (OR 1.53, CI 1.25-1.89), substance abuse and dependence (OR 1.45, CI 1.29-1.63), psychological diseases and mental disorders (OR 1.28, CI 1.18-1.39) and for one condition with a case prevalence of 14.7%, diabetes (OR 1.28, CI 1.20-1.36). CONCLUSIONS: In Sweden, in the current generation of older drivers, acknowledged driving-impairing medical conditions at the national and European levels remain a concern. After adjustment for one another, all but 2 of the conditions are associated with RTCs albeit to varying degrees and more pronounced in the age group 65-79 compared to 80 or older. To promote and sustain older people's mobility, addressing this issue will require a blend of interventions where, hopefully, technological and infrastructural innovations may help counteracting individual health-related shortcomings.

Injury crashes and the relationship with disease causing excessive daytime sleepiness.

OBJECTIVE: The objective of this study was to understand the relationship between some of the most common diseases that are known to contribute to excessive daytime sleepiness (EDS) and traffic injury crashes. Specific focus was on the relationship between disease and crash type (single-vehicle or multiple-vehicle crash) and between disease and injury severity. METHODS: This registry-based study considered all passenger car drivers involved in a crash in Sweden between 2011 and 2016 who were 40 years or older at the time of the crash (n = 54,090). For each crash-involved driver, selected medical diagnoses registered from 1997 until the day before the crash were extracted from the National Patient Register. The drivers were assigned to 1 of 4 groups, depending on prior diseases: sleep apnea (SA; group 1, n = 2,165), sleep disorders (group 2, n = 724), Parkinson's or epilepsy (group 3, n = 645) and a reference group (group 4, n = 50,556). Logistic regression analysis compared single-vehicle crashes with multiple-vehicle crashes and moderately/severely injured drivers with slightly/uninjured drivers. RESULTS: Drivers with EDS-related diseases (groups 1-3) had higher probability of a single-vehicle crash than a multiple-vehicle crash compared to the reference group. The most sizeable effect was found for Parkinson's/epilepsy with an odds ratio (OR) of 2.5 (confidence interval [CI], 2.1-3.0). For multiple-vehicle crashes, the probability of a moderate/severe injury was higher for drivers with other sleep disorders (OR = 1.5; CI, 1.0-2.2) and Parkinson's/epilepsy (OR = 1.6; CI, 1.1-2.3) compared to the reference group. CONCLUSIONS: This study has made first steps toward understanding the relationship between some of the most common diseases that are known to contribute to EDS and crashes. Having Parkinson's/epilepsy, in particular, elevated the probability of a single-vehicle crash compared to a multiple-vehicle crash. A single-vehicle crash was seen as indicative of causing a crash; thus, having Parkinson's/epilepsy could be interpreted as a risk factor for crash involvement. Having Parkinson's/epilepsy, as well as other sleep disorders, was also related to more severe outcomes in multiple-vehicle crashes, given that a crash occurred. This was not identified in single-vehicle crashes.

A pattern analysis of traffic crashes fatal to older drivers.

A synthesis of the various crash circumstances in which older drivers die is lacking. This study is based on data from Sweden's national archive of fatal RTCs, and focuses on crashes in which the deceased driver was aged 65+ (2002-2004; n=152). Crash patterns were identified by means of cluster analysis using a sub-set of 12 variables describing both driver and crash event characteristics. Crashes where the driver had died of natural causes prior to crash made up 19.7% of the cases (30 crashes) and were mainly single crashes. Four additional clusters were also identified. Two involved making left turns at intersections, one over-represented among men, occurring typically at weekends, in low-speed areas (30.6%), and the second one, over-represented among women, consisting of crashes in dry road conditions, and on intermediate-speed roads (21.5%). A third cluster included head-on and single-vehicle crashes occurring in dry road conditions but on high-speed roads (29.8%). The last cluster consisted of crashes occurring during the winter and on high-speed roads (18.2%). Older drivers die in traffic in various circumstances, sometimes prior to crashing. Some circumstances cannot be easily alleviated but others could, e.g., through modifications of the road traffic environment and car active safety measures that can help compensate for age-related shortcomings.