Elvik R.,Norwegian Institute of Transport Economics
Accident Analysis and Prevention | Year: 2011
This paper shows that the meta-analysis of bicycle helmet efficacy reported by Attewell, Glase, and McFadden (Accident Analysis and Prevention 2001, 345-352) was influenced by publication bias and time-trend bias that was not controlled for. As a result, the analysis reported inflated estimates of the effects of bicycle helmets. This paper presents a re-analysis of the study. The re-analysis included: (1) detecting and adjusting for publication bias by means of the trim-and-fill method; (2) ensuring the inclusion of all published studies by means of continuity corrections of estimates of effect rely on zero counts; (3) detecting and trying to account for a time-trend bias in estimates of the effects of bicycle helmets; (4) updating the study by including recently published studies evaluating the effects of bicycle helmets. The re-analysis shows smaller safety benefits associated with the use of bicycle helmets than the original study. © 2011 Elsevier Ltd All rights reserved.
Hoye A.,Norwegian Institute of Transport Economics
Accident Analysis and Prevention | Year: 2013
The present study has replicated the results from a previous meta-analysis by Erke (2009) [Erke, A., 2009. Red light for red-light cameras? A meta-analysis of the effects of red-light cameras on crashes. Accident Analysis & Prevention 41 (5), 897-905.] based on a larger sample of RLC-studies, and provides answers to the criticisms that were raised by Lund et al. (2009) [Lund, A.K., Kyrychenko, S.Y., Retting, R.A., 2009. Caution: a comment on Alena Erke's red light for red-light cameras? A meta-analysis of the effects of red-light cameras on crashes. Accident Analysis and Prevention 41, 895-896.] against the previous meta-analysis. The addition of recent studies to the meta-analysis and a more thorough investigation of potential moderator variables lead to a slight improvement of the estimated effects of RLC in the previous meta-analysis. The present study found a non-significant increase of all crashes by 6% and a non-significant decrease of all injury crashes by 13%. Right-angle collisions were found to decrease by 13% and rear-end collisions were found to increase by 39%. For right-angle injury collisions a decrease by 33% was found and for rear-end injury collisions a smaller increase was found (+19%). The effects of RLC are likely to be more favorable when RLC-warning signs are set up at main entrances to areas with RLC enforcement than when each RLC-intersection is signposted. The effects of RLC may become more favorable over time, this could however not be investigated empirically. Several results indicate that spillover effects may occur for right-angle collisions, but most likely not for rear-end and other crashes. If spillover effects do not occur for rear-end crashes, which increase at RLC intersection, this would be a positive result for RLC. However, the results seem to be affected to some degree by publication bias and the effects may therefore be somewhat less favorable than indicated by the results from meta-analysis. © 2013 Elsevier Ltd. All rights reserved.
Hjorthol R.,Norwegian Institute of Transport Economics
Ageing and Society | Year: 2013
Previous research has shown that mobility and the ability to leave the home are among the essential aspects of older people's quality of life. However, surveys of older people's access to transport resources and the impact of mobility on welfare and wellbeing are few. Many previous studies are based on small samples or qualitative data. The questions addressed in this paper are how transport resources are distributed among different groups of older people, to which degree the transport needs of these groups are met and how this is related to their wellbeing. The empirical analysis is based on a Norwegian nationwide survey among 4,723 respondents 65 years and older. The respondents were asked about their access to transport resources, both private and public, health problems connected to use of transport modes, their daily activities and mobility, their uncovered transport needs and the importance of different activities for their life quality. The analysis reveals great differences between groups; especially between men and women, but also between different age groups and by different place of living. The special transport offered by the local authorities is seen as insufficient, and with increasing age a great deal of older people have low mobility and an uncovered transport need that reduces their life quality. © Cambridge University Press 2012.
Elvik R.,Norwegian Institute of Transport Economics
Accident Analysis and Prevention | Year: 2010
This paper examines the stability of long-term trends in the number of traffic fatalities in eight highly motorised countries: Norway, Sweden, Denmark, Finland, The Netherlands, Great Britain, Australia and The United States. In all these countries, the number of traffic fatalities reached a peak around 1970-1972 and has since declined. The decline has, however, been irregular and fairly long periods of stagnation or even increase in the number of fatalities have occurred in all countries. A stable trend is defined in this paper as a trend that remains unchanged and therefore can be used to successfully predict the future number of fatalities by means of extrapolation. It is concluded that the trends towards fewer fatalities in the countries selected have not been stable and that even trend lines that fit past trends very closely are usually worthless for predictive purposes. An attempt was made to identify factors influencing long-term trends by fitting negative binomial regression models to fatality data. Although some of the models fitted the data marginally better than simple trend lines, these models are not necessarily more useful for predicting future trends than simple trend lines, since using the models for prediction requires that future changes in all explanatory variables must be predicted. The chief lesson is that past trends do not provide a reliable basis for predicting future developments with respect to the number of traffic fatalities. © 2009 Elsevier Ltd. All rights reserved.
Vaa T.,Norwegian Institute of Transport Economics
Accident Analysis and Prevention | Year: 2014
The present meta-analysis is based on 16 studies comprising 32 results. These studies provide sufficient data to estimate relative accident risks of drivers with ADHD. The overall estimate of relative risk for drivers with ADHD is 1.36 (95% CI: 1.18; 1.57) without control for exposure, 1.29 (1.12; 1.49) when correcting for publication bias, and 1.23 (1.04; 1.46) when controlling for exposure. A relative risk (RR) of 1.23 is exactly the same as found for drivers with cardiovascular diseases. The long-lasting assertion that "ADHD-drivers have an almost fourfold risk of accident compared to non-ADHD-drivers", which originated from Barkley et al.'s study of 1993, is rebutted. That estimate was associated with comorbid Oppositional Defiant Disorder (ODD) and/or Conduct Disorder (CD), not with ADHD, but the assertion has incorrectly been maintained for two decades. The present study provides some support for the hypothesis that the relative accident risk of ADHD-drivers with comorbid ODD, CD and/or other conduct problems, is higher than that of ADHD-drivers without these comorbidities. The estimated RRs were 1.86 (1.27; 2.75) in a sample of ADHD-drivers in which a majority had comorbid ODD and/or CD compared to 1.31 (0.96; 1.81) in a sample of ADHD-drivers with no comorbidity. Given that ADHD-drivers most often seem to drive more than controls, and the fact that a majority of the present studies lack information about exposure, it seems more probable that the true RR is lower rather than higher than 1.23. Also the assertion that ADHD-drivers violate traffic laws more often than other drivers should be modified: ADHD-drivers do have more speeding violations, but no more drunk or reckless driving citations than drivers without ADHD. All accident studies included in the meta-analysis fail to acknowledge the distinction between deliberate violations and driving errors. The former are known to be associated with accidents, the latter are not. A hypothesis that ADHD-drivers speed more frequently than controls because it stimulates attention and reaction time is suggested. © 2013 Elsevier Ltd. All rights reserved.