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The effect of the Swedish bicycle helmet law for children: An interrupted time series study
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences. (Centrum för Personsäkerhet)ORCID iD: 0000-0002-1189-9950
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences. (Centrum för Personsäkerhet)
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.ORCID iD: 0000-0002-0293-1795
2014 (English)In: Journal of Safety Research, ISSN 0022-4375, E-ISSN 1879-1247, Vol. 51, 15-22 p.Article in journal (Refereed) Published
Abstract [en]

Previous population-based research has shown that bicycle helmet laws can reduce head injury rates among cyclists. According to deterrence theory, such laws are mainly effective if there is a high likelihood of being apprehended. In this study, we investigated the effect of the Swedish helmet law for children under the age of 15, a population that cannot be fined. Method  An interrupted time series design was used. Monthly inpatient data on injured cyclists from 1998–2012, stratified by age (0–14, 15 +), sex, and injury diagnosis, was obtained from the National Patient Register. The main outcome measure was the proportion of head injury admissions per month. Intervention effect estimates were obtained using generalized autoregressive moving average (GARMA) models. Pre-legislation trend and seasonality was adjusted for, and differences-in-differences estimation was obtained using adults as a non-equivalent control group. Results There was a statistically significant intervention effect among male children, where the proportion of head injuries dropped by 7.8 percentage points. There was no evidence of an intervention effect on the proportion of head injuries among female children. Conclusion According to hospital admission data, the bicycle helmet law appears to have had an effect only on male children.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2014. Vol. 51, 15-22 p.
Keyword [en]
helmet law, cyclist, accident, injury rate, children, patient, swedish
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Research subject
Public Health Science
Identifiers
URN: urn:nbn:se:kau:diva-30119DOI: 10.1016/j.jsr.2014.07.001ISI: 000345723400003PubMedID: 25453172OAI: oai:DiVA.org:kau-30119DiVA: diva2:666160
Available from: 2013-11-22 Created: 2013-11-22 Last updated: 2016-04-28Bibliographically approved
In thesis
1. Searching for causal effects of road traffic safety interventions: applications of the interrupted time series design
Open this publication in new window or tab >>Searching for causal effects of road traffic safety interventions: applications of the interrupted time series design
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Traffic-related injuries represent a global public health problem, and contribute largely to mortality and years lived with disability worldwide. Over the course of the last decades, improvements to road traffic safety and injury surveillance systems have resulted in a shift in focus from the prevention of motor vehicle accidents to the control of injury events involving vulnerable road users (VRUs), such as cyclists and moped riders. There have been calls for improvements to the evaluation of safety interventions due to methodological problems associated with the most commonly used study designs. The purpose of this licentiate thesis was to assess the strengths and limitations of the interrupted time series (ITS) design, which has gained some attention for its ability to provide valid effect estimates. Two national road safety interventions involving VRUs were selected as cases: the Swedish bicycle helmet law for children under the age 15, and the tightening of licensing rules for Class 1 mopeds. The empirical results suggest that both interventions were effective in improving the safety of VRUs. Unless other concurrent events affect the treatment population at the exact time of intervention, the effect estimates should be internally valid. One of the main limitations of the study design is the inability to identify why the interventions were successful, especially if they are complex and multifaceted. A lack of reliable exposure data can also pose a further threat to studies of interventions involving VRUs if the intervention can affect the exposure itself. It may also be difficult to generalize the exact effect estimates to other regions and populations. Future studies should consider the use of the ITS design to enhance the internal validity of before-after measurements.

Abstract [en]

Traffic-related injuries represent a global public health problem, and contribute largely to mortality and years lived with disability. Over the course of the last decades, improvements to road traffic safety and injury surveillance systems have resulted in a shift in focus from motor vehicle accidents to injury events involving vulnerable road users (VRUs), such as cyclists and moped riders. There have been calls for improvements to the evaluation of safety interventions due to methodological problems associated with the most commonly used study designs. The purpose of this licentiate thesis was to assess the strengths and limitations of the interrupted time series (ITS) design, which has gained some attention for its ability to provide valid effect estimates while accounting for secular trends. Two national interventions involving VRUs were selected as cases: the Swedish bicycle helmet law for children under the age 15, and the tightening of licensing rules for Class 1 mopeds. The empirical results suggest that both interventions were effective. These results are discussed in the light of some methodological considerations regarding internal and external validity, data quality and the ability to fully understand key causal mechanisms behind complex interventions. 

Place, publisher, year, edition, pages
Karlstad: Karlstad University Press, 2015. 80 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2015:22
Keyword
Causal inference, Repeated measures, Methodology, Econometrics, Injury Epidemiology, Vulnerable Road Users, Time series analysis
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Research subject
Risk and Environmental Studies
Identifiers
urn:nbn:se:kau:diva-35781 (URN)978-91-7063-638-7 (ISBN)
Presentation
2015-05-22, Fryxellsalen, 1B 306, Karlstads universitet, 13:00 (Swedish)
Opponent
Supervisors
Funder
Swedish Civil Contingencies Agency, 2013-4176
Available from: 2015-04-28 Created: 2015-04-08 Last updated: 2015-04-28Bibliographically approved
2. Assessing the effects of societal injury control interventions
Open this publication in new window or tab >>Assessing the effects of societal injury control interventions
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Injuries have emerged as one of the biggest public health issues of the 21th century. Yet, the causal effects of injury control strategies are often questioned due to a lack of randomized experiments. In this thesis, a set of quasi-experimental methods are applied and discussed in the light of causal inference theory and the type of data commonly available in injury surveillance systems. I begin by defining the interrupted time series design as a special case of the regression-discontinuity design, and the method is applied to two empirical cases. The first is a ban on the sale and production of non-reduced ignition propensity (RIP) cigarettes, and the second is a tightening of the licensing rules for mopeds. A two-way fixed effects model is then applied to a case with time-varying starting dates, attempting to identify the causal effects of municipality-provided home help services for the elderly. Lastly, the effect of the Swedish bicycle helmet law is evaluated using the comparative interrupted time series and synthetic control methods. The results from the empirical studies suggest that the stricter licensing rules and the bicycle helmet law were effective in reducing injury rates, while the home help services and RIP cigarette interventions have had limited or no impact on safety as measured by fatalities and hospital admissions. I conclude that identification of the impact of injury control interventions is possible using low cost means. However, the ability to infer causality varies greatly by empirical case and method, which highlights the important role of causal inference theory in applied intervention research. While existing methods can be used with data from injury surveillance systems, additional improvements and development of new estimators specifically tailored for injury data will likely further enhance the ability to draw causal conclusions in natural settings. Implications for future research and recommendations for practice are also discussed.

Abstract [en]

Injuries have emerged as one of the biggest public health issues of the 21th century. Yet, the causal effects of injury control strategies are rarely known due to a lack of randomized experiments. In this thesis, a set of quasi-experimental methods are discussed in the light of causal inference theory and the type of data commonly available in injury surveillance systems. I begin by defining the identifying assumptions of the interrupted time series design as a special case of the regression-discontinuity design, and the method is applied to two empirical cases. The first is a ban on the sale and production of non-fire safe cigarettes and the second is a tightening of the licensing rules for mopeds. A fixed effects panel regression analysis is then applied to a case with time-varying starting dates, attempting to identify the causal effects of municipality-provided home help services for the elderly. Lastly, the causal effect of the Swedish bicycle helmet law is evaluated using a comparative interrupted time series design and a synthetic control design. I conclude that credible identification of the impact of injury control interventions is possible using simple and cost-effective means. Implications for future research and recommendations for practice are discussed.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2016. 59 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2016:23
Keyword
causal inference, epidemiology, injury, time series analysis, impact evaluation
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Research subject
Risk and Environmental Studies
Identifiers
urn:nbn:se:kau:diva-41204 (URN)978-91-7063-701-8 (ISBN)
External cooperation:
Public defence
2016-05-19, Eva Erikssonsalen, 21A342, Karlstad, 13:00 (Swedish)
Opponent
Supervisors
Funder
Swedish Civil Contingencies Agency
Available from: 2016-04-29 Created: 2016-04-01 Last updated: 2016-08-25Bibliographically approved

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Bonander, CarlNilson, FinnAndersson, Ragnar
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